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ASAR Data Formats Products
Geolocation Grid ADSRs
Doppler Centroid parameters
Chirp parameters
Antenna Elevation pattern
ASAR external characterization data
ASAR external calibration data
Level 0 SPH
Level 0 MDSR
SPH for auxiliary data with N=1 DSDs
Wave Mode Geolocation ADS
ASAR Wave Mode Products Base SPH
Slant Range to Ground Range conversion parameters
Measurement Data Set containing spectra. 1 MDSR per spectra.
Ocean Wave Spectra
Map Projection parameters
ASAR Image Products SPH
Measurement Data Set 1
Auxilliary Products
ASA_XCH_AX: ASAR External characterization data
ASA_XCA_AX: ASAR External calibration data
ASA_INS_AX: ASAR Instrument characterization
ASA_CON_AX: ASAR Processor Configuration
Browse Products
ASA_WS__BP: ASAR Wide Swath Browse Image
ASA_IM__BP: ASAR Image Mode Browse Image
ASA_GM__BP: ASAR Global Monitoring Mode Browse Image
ASA_AP__BP: ASAR Alternating Polarization Browse Image
Level 0 Products
ASA_WV__0P: ASAR Wave Mode Level 0
ASA_WS__0P: ASAR Wide Swath Mode Level 0
ASA_MS__0P: ASAR Level 0 Module Stepping Mode
ASA_IM__0P: ASAR Image Mode Level 0
ASA_GM__0P: ASAR Global Monitoring Mode Level 0
ASA_EC__0P: ASAR Level 0 External Characterization
ASA_APV_0P: ASAR Alternating Polarization Level 0 (Cross polar V)
ASA_APH_0P: ASAR Alternating Polarization Level 0 (Cross polar H)
ASA_APC_0P: ASAR Alternating Polarization Level 0 (Copolar)
Level 1 Products
ASA_IMS_1P: ASAR Image Mode Single Look Complex
ASA_IMP_1P: ASAR Image Mode Precision Image
ASA_IMM_1P: ASAR Image Mode Medium Resolution Image
ASA_IMG_1P: ASAR Image Mode Ellipsoid Geocoded Image
ASA_GM1_1P: ASAR Global Monitoring Mode Image
ASA_APS_1P: ASAR Alternating Polarization Mode Single Look Complex
ASA_APP_1P: ASAR Alternating Polarization Mode Precision Image
ASA_APM_1P: ASAR Alternating Polarization Medium Resolution Image product
ASA_WSS_1P: Wide Swath Mode SLC Image
ASA_WVS_1P: ASAR Wave Mode Imagette Cross Spectra
ASA_WSM_1P: ASAR Wide Swath Medium Resolution Image
ASA_APG_1P: ASAR Alternating Polarization Ellipsoid Geocoded Image
Level 2 Products
ASA_WVW_2P: ASAR Wave Mode Wave Spectra
ASAR Glossary Terms
Sea Ice Glossary
Land Glossary
Oceans Glossary
Geometry Glossary
ASAR Instrument Glossary
Acronyms and Abbreviations
ASAR Frequently Asked Questions
The ASAR Instrument
Instrument Characteristics and Performance
Inflight Performance Verification
Preflight Characteristics and Expected Performance
Instrument Description
Internal Data Flow
ASAR Instrument Functionality
Payload Description and Position on the Platform
ASAR Products and Algorithms
Auxiliary Products
Common Auxiliary Data Sets
Auxiliary Data Sets for Level 1B Processing
Summary of Auxiliary Data Sets
Instrument-specific Topics
Level 2 Product and Algorithms
Level 2 Product
ASAR Level 2 Algorithms
Level 1B Products
ASAR Level 0 Products
Level 0 Instrument Source Packet Description
Product Evolution History
Definitions and Conventions
Organisation of Products
ASAR Data Handling Cookbook
Hints and Algorithms for Higher Level Processing
Hints and Algorithms for Data Use
ASAR Characterisation and Calibration
The Derivation of Backscattering Coefficients and RCSs in ASAR Products
External Characterisation
Internal Calibration
Pre-flight Characterisation Measurements
ASAR Latency Throughput and Data Volume
Data Volume
Products and Algorithms Introduction
Child Products
The ASAR User Guide
Image Gallery
Further Reading
How to Use ASAR Data
Software Tools
How to Choose ASAR Data
Special Features of ASAR
Geophysical Coverage
Principles of Measurement
Scientific Background
Geophysical Measurements
ASAR Product Handbook
ASAR instrument characterization data
Wave Mode processing parameters
ASAR processor configuration data
Main Processing parameters
ASA_WVI_1P: ASAR Wave Mode SLC Imagette and Imagette Cross Spectra
Product Terms
RADAR and SAR Glossary
Level 1B Products
Summary of Applications vs Products
Site Map
Frequently asked questions
Terms of use
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5.3 Product Terms

Table 5.3
Alternating Polarisation Mode (APP) Product

Two co-registered images per acquisition,from any of 7 selectable swaths.HH/VV HH/HV or VV/VH polarisation pairs possible.Spatial resolution of approximately 30 m (for Precision product) ( see also "Organisation of Products" ). These products are similar to Image Mode (IM) products but include a second image acquired using a second polarisation combination. The raw data is acquired in bursts of alternating polarisation. (See also Burst Mode Products )

Alternating Polarisation Browse (APB) Image

Alternating Polarisation Browse (APB) image is a low-resolution compressed image product that will be produced systematically together with the AP Medium-resolution product.

( see also "Organisation of Products" and "Browse Products" )

Alternating Polarisation Medium-Resolution (APM) product This product is systematically generated in the PDHS from Level 0 data collected when the instrument is in alternating polarisation (AP) mode. The product is processed to approximately 150 m resolution using the SPECAN algorithm and contains radiometric resolution good enough for ice applications. The product contains one image corresponding to one of the 4 possible polarisation combinations (HH, VV, HV, or VH) when processed systematically in near real-time (NRT). This product may also be generated on request with one, or both, polarisations included in the product. ( See also "Organisation of Products" )
Alternating Polarisation Mode Ellipsoid Geocoded (APG) image

The Alternating Polarisation Mode Ellipsoid Geocoded (APG) image is a multi-look image generated upon request using the SPECAN algorithm and the most up to date auxiliary information available at the time of processing.

( see also "Organisation of Products" and "Level 1B Image Products" )

Alternating Polarisation Mode Single-look Complex (APS) image

The Alternating Polarisation Mode Single-look Complex (APS) image is a stand-alone narrow swath product uses the Range Doppler algorithm and the most up to date processing parameters available at the time of processing.

( see also "Organisation of Products" and "Level 1B Image Products" )

Annotation Data Set (ADS) One of two types of data sets ( Measurement Data Sets (MDS) is the other ) found in the Data Set Records (DSRs) of an ASAR product. See "Definitions and Conventions"
Annotated Instrument Source Packet (AISP) The Level 0 product contains Annotated Instrument Source Packets (AISPs). These are Instrument Source Packets (ISPs) as received from the instrument, with a small header attached by the Front End Processor (FEP).
Antenna Elevation Gain Scaling Factor ( See Antenna Elevation Gain Correction )
Antenna Elevation Pattern The antenna pattern is the gain of a signal transmitted or received by the antenna, as a function of angle. The Elevation Pattern is the antenna pattern in the elevation, or vertical, direction.
Antenna Elevation Gain Correction Antenna elevation gain correction is derived by processing the periodic calibration data. Periodic calibration generates calibration data for the 32 rows of the SAR antenna in a cyclic manner and downlinks this data interspersed with the imaging data. The antenna gain correction is derived from the calibration data from all 32 antenna rows received over a period of time.

The elevation gain correction is also updated whenever a new periodic calibration cycle is found in the input data.

ASAR Modes The different operating/measurement modes of the ASAR instrument. They are Image (IM) Mode , Alternating Polarisation (AP) Mode, Wide Swath (WS) Mode, Global Monitoring (GM) Mode, and the Wave (WV) Mode. (See "Products and Algorithms Introduction")
Attachment Flag Attachment flags are used within the DSRs of ASAR products. See "Definitions and Conventions"2.13
Auxiliary Data Product Data other than the instrument measurements which are necessary to the processing. Auxiliary data may come from the satellite itself, sources external to the PDS, or be created by instrument processing facilities within the PDS. ( see also "Auxiliary Products" 2.9. )
Average Cross Correlation Coefficient (ACCC) The Cross Correlation Coefficient that is measured in the Doppler centroid estimation algorithm is measured in the azimuth direction. The Average Cross Correlation Coefficient (ACCC) is the average of this Cross Correlation Coefficient over several azimuth lines.
Azimuth Compression Azimuth compression is a matched filtering of the azimuth signal, performed efficiently using FFT's. See discussion on "Azimuth Compression" in the section entitled Range Doppler in chapter 2.
Azimuth Bin An azimuth bin refers to a particular azimuth sample number.
Azimuth Fast Fourier Transform ( FFT ) FFTs are performed in the azimuth direction. The FFT length must be as least twice as long as the azimuth block size to achieve the oversampling that is necessary prior to detection. See section entitled "Range Doppler" in chapter 2.
Azimuth Look Extraction The good points for each azimuth look are selected.
Azimuth Reference Function Multiply (deramp): The data is multiplied by the azimuth reference function. See also Deramping.
Azimuth Resolution Resolution characteristic of the azimuth dimension, usually applied to the image domain. Azimuth resolution is fundamentally limited by the Doppler bandwidth of the system. Excess Doppler bandwidth is usually used to allow extra looks, at the expense of azimuth resolution.
Bin A bin refers to a certain sample of a signal, in the time domain or the frequency domain.
Block Adaptive Quantisation (BAQ) decoding A table look-up operation is used to perform BAQ decoding. The operation decompresses the data from the 2 or 4 bit coded representation to the 8 bit representation. Data compression using Block Adaptive Quantisation depends on the signals being quasi-random with Gaussian probability distribution function. The calibration pulses are completely deterministic and hence do not follow this assumption. For this the BAQ is effectively switched off giving 8 bits per sample quantisation -the highest accuracy possible.
Browse Averaging The medium-resolution image is averaged and subsampled to form a browse product. Also referred to as Block Averaging.
Browse Product Browse products are severely decimated images which can be ordered from the ENVISAT inventory. These products are very small, to support electronic transmission while querying the catalogues. They may be further reduced in size through the use of standardised data compression algorithms. Browse products are produced systematically, as by-products of the generation of the medium-resolution Level 1B Image products, and contain image lines derived from a data segment (up to a full orbit of data). ( see also "Browse Products" )
Burst Mode Products

Image products that are formed with the SPECAN algorithm are formed from periodic bursts of SAR data. The burstiness may arise because of the way the data is collected, as in Alternating Polarisation (AP) mode or ScanSAR modes [Global Monitoring (GM), Wide Swath(WS)], or bursts may be extracted during processing, as in the formation of medium-resolution Image Mode (IM) products. Typically a burst is much shorter than the time it takes the azimuth beam to pass over a point on the ground (synthetic aperture time). In comparison with the conventional stripline imaging methods, burst mode operation enables a reduced power consumption, and data rate, at the expense of the resolution and image quality achieved.

When the burst images are stitched together to form the image product, the periodic intensity variation is seen as scalloping in the image. Scalloping can be corrected by multiplication with a descalloping function.

Butterworth Filter A particular type of filter frequency response, which is smooth (no ripples) as a function of frequency.
Calibration Process of comparing an instrument's measurement with that of a known standard. For a discussion on this topic see "ASAR Characterisation and Calibration" 2.11. in chapter 2 and "In-flight Performance Verification." 3.2.2. in chapter 3.
Calibration Data ASAR calibration data is considered to be auxiliary data within the PDS. The data may be from Internal ( Instrument ) Calibration, External Characterisation, or External Calibration.
Child Product A child is the result of the extraction of a set of data from a parent product (Level 0, Level 1B, Level 2). Generation of child products can be formulated in terms of time, data set (DS), or ISP selection; in terms of either segments or scenes.
Complex Factor (fnp) The fnp is the ground characterised complex factor characterising the path through the calibration loop and from the calibration coupler to the antenna face for row n, polarisation p at the swath reference angle for each beam. It is used in calculating the elevation gain
function and to reconstruct the replica.
Complex Loop Paths Characterisation Factor (gnp) The gnp is the complex loop paths characterisation factor relative to free space, where n is the index of the row (1 to 32) and p is the index of the polarisation (H or V). As with the Complex Factor (fnp) it is used in calculating the elevation gain function and to reconstruct the replica.
Complex Product In a complex product, the extracted frequency array for each look is multiplied by the matched filter frequency response and inverse FFT'd to form the complex look image. The matched filter frequency response is adjusted by a small linear phase ramp for each look. This is equivalent to shifting the compressed look in time, and is required to ensure that the images from different looks are aligned properly for look summation. The amount of azimuth shift is range-dependent. In addition, azimuth interpolation may also performed after look compression to achieve a desire azimuth pixel spacing, and it is done on each look separately. ( see also Detected Product )
Compression Compression refers to the matched filtering of a linear FM pulse, in which all the energy of a long duration input pulse is gathered together at a peak value of a narrow output pulse.
Compression Algorithm

The compression algorithm that handles the necessary pulse compression. See the discussion on "Pulse Compression" in chapter 2 entitled "ASAR Level 1B Algorithm Physical Justification".

Cross Correlation Coefficient (CCC) The Cross Correlation Coefficient (CCC) is used in the Doppler centroid estimation algorithm. It is the average value of the product of adjacent signal samples, where the sample of a signal is multiplied by the conjugate of the next sample.

Cross Covariance

The average of the product of two signals, with one signal conjugated and shifted with respect to the other. The cross covariance is a function of the relative shift and is used to obtain the cross spectrum for the Level 1B wave products.
Cross Spectra The cross spectrum is the Fourier transform of the cross covariance.
Data Set (DS)

Data Sets are in mixed-binary format and each consists of one or more Data Set Records (DSRs). (See also "Definitions and Conventions ")

Data Set Descriptor (DSD) Data Set Descriptors are used to describe an attached Data Set or to provide reference to external files relevant to the current product (e.g. auxiliary data used in processing but not included with the product). There must be one DSD per Data Set or per reference to an external file. ( see also "Definitions and Conventions ")
Data Set Record (DSR) Data Set Records contain information about products or auxiliary data. A number of records types are defined and used according to the type of product.
Deramping A process whereby burst data is multiplied by the azimuth reference function. See discussion on "Azimuth Processing" in the section entitled "SPECAN" in chapter 2.
Descalloping Descalloping is a radiometric correction of the burst image, performed with a vector multiply in the azimuth direction. See Scalloping . For a further discussion on this topic see the section entitled "Descalloping" in chapter 2.
Deskew The data is shifted to correct for the skew that was applied during linear RCMC. Only the integer portion is corrected in this step. The fractional portion is handled during the SR/GR resampling step.
Detected Product ( see also Complex Product ). For the detected (magnitude) image products (IMP, IMG), a technique called multilooking is incorporated into the algorithm. In this method, separate images are formed from different azimuth spectral bands (looks), and the magnitude look images are averaged to reduce speckle. See also Detection in Radar and SAR glossary.
Digital Operating on data represented as a series of binary digits.
Directional Bins The two-dimensional cross spectrum is converted to polar format, with dimensions of wavenumber and direction. A directional bin refers to a sample of the cross spectrum in at a certain direction.
Doppler Ambiguity Resolver (DAR) Mathematical model used to determine the Doppler Ambiguity. See chapter 2 "Doppler Frequency Estimator" .
Ellipsoid Geocoded Product The Ellipsoid Geocoded Image product is similar to a Precision Image, but with the best available instrument corrections applied for precise location and rectification to a map projection.
Extracted Calibration Product (ECP) The Extracted Calibration Product (ECP) is a child product extracted from a level-0 product. It contains a suite of complete ISPs for a selected time interval, and its structure is the same as the parent level-0 product.
Extracted Instrument Header (EIH) The Extracted Instrument Header (EIH) child product is extracted from a level-0 product. It contains a suite of ISP fields for a selected time interval. It contains an MPH, SPH and MDS.
False Colour (FC) Using one colour to represent another. A colour imaging process which produces an image of a colour that does not correspond to the true colour of the scene (as seen by our eyes).
False Colour Composite (FCC) An image produced by displaying multiple spectral bands as colours different from the spectal range they were taken in. It is a method of displaying multi-band (multi-channel) imagery. By assigning three of the image bands to the fundamental colours red, blue and green, you can produce a colour image. The blue band in the original image is often affected by atmospheric effects such as haze, and is therefore usually left out. When the assigned image bands do not correspond to the frequencies of red, blue and green the output image will appear in colours that are not intuitive or natural. For instance, different types of vegetation might appear as blue, red, green or yellow. Intuitively, vegetation would appear green. Such an image is known as a false colour composite. It is useful for extraction information difficult to discern in the original imagery, variations in vegetation species or health, for example.
Fast Fourier Transform (FFT)

A mathematical operation that fits a continuous function through the discrete digital number values, if they were plotted along each row and column of an image. The peaks and valleys along any given row or column can be described mathematically by a combination of sine and cosine waves with various amplitudes, frequencies, and phases. A Fourier Transform results from the calculation of the amplitude and phase for each possible spatial frequency in an image.

After an image is separated into its component spatial features, it is possible to display these values in a two-dimentional scatter plot, known as a Fourier Spectrum.

Floating Scene Floating scene concept on archived products
Flexible Block Adaptive Quantisation (FBAQ) Method Process used to reduce echo samples. The FBAQ algorithm is an optimum minimum mean square quantizer, meaning it minimizes the value of the mean square of the differences between the original signal data and the FBAQ decoded signal data. One of the properties of this type of quantizer is that the variance of the decoded signal is reduced compared to that of the original signal. (See also Block Adaptive Quantisation (BAQ) decoding and Root Mean Squared (RMS) Equalisation )
Frame The set of product pixels corresponding to a given satellite position
Frequency Domain The representation is the Fourier transform of the original distribution.
For every distribution f in time there is an equivalent representation F whose independent variable is frequency. F and f are equivalent in the sense that they carry the same information, but expressed in an alternative way. The concept is often generalised to distributions in the space domain, for which the Fourier transform is in the spatial frequency domain, having units of cycles per unit length. The azimuth frequency domain is also known as the Doppler domain.
Fully Consolidated Product This is a Level 1B ASAR product generated off-line, time ordered, no overlap, no data gaps (except where the instrument has been turned off), fully validated; the basis for any further off-line processing. It has been produced using the most precise auxiliary information available. It is compiled to respect the defined product boundaries (e.g., ascending node to ascending node at the equator for full orbit products).
Gaussian Filter A filter with a Gaussian-shaped frequency response.
Geocoded Geographic correction of image data to conform to a map projection. It is the process of resampling the data to conform to a standard map projection with known co-ordinates. Ground Control Points (GCPs) are often used to increase the accuracy of the geocoding process. ( See also ).
Geolocation Geolocation information is provided in the product header in the form of latitude and longitude information that allow the user to determine the area covered by the data from a simple inspection of the header. For image data, a location grid may also be provided as an attachment to the product to allow for precise pixel geolocation.
Geophysical Calibration Constant (CMOD) The Geophysical Calibration Constant (CMOD) is an algorithm used for estimating the wind speed from the amplitude of the SAR image. In the Level 2 wave mode algorithm the parameter is used as follows:

sigmaNought = sin(thetaMid) * meanVal / kCmod;

In this equation:

sigmaNought is the (modelled) radar cross section of the sea surface; thetaMid is the incidence angle at the centre of the imagette, and meanVal is the mean intensity of the imagette. Therefore, kCmod is simply the expected value of :

kCmod = sin(thetaMid) * meanVal / sigmaNought

Georeferenced The act of registering a map's co-ordinates with the ground's co-ordinates at true scale, also incorporating latitude and longitude information into the image.
Ghosting A SAR image artefact where a dim copy of a bright target appears offset in range and/or azimuth. Ghosts are visible in the background as dark and invariant (e.g. calm water). Alternatively, ghosts are difficult to detect over variable backgrounds (e.g. forest). Ghosts occur when the desired signal is contaminated by the signal of adjacent targets. There are three types of ghosts: azimuth ambiguity, range ambiguity and nadir ambiguity..
Global Annotation Data Set Annotation data set (ADS) which applies to the entire product.
Global Coverage A global product contains coverage for the entire length of an orbit.
Global Monitoring Product Mode (GM) The Global-Monitoring Mode product is a 1 km (low-) resolution image with a 405 km swath width, suitable for dissemination by electronic links in near real-time (NRT). ( see also "Organisation of Products" )
Global Monitoring Mode Browse (GMB) Image Product

The Global Monitoring Mode Browse (GMB) Image product is a low-resolution product will be produced systematically together with the GM Image Product from Level 0 GM data.

( see also "Organisation of Products" and "Browse Products" )

Global Monitoring Mode (GMI) Image Product This is the standard product for ASAR Global Monitoring Mode. It is processed to approximately 1 km resolution using the SPECAN algorithm. The swath width is approximately 400 km. ( see also "Organisation of Products" )
Granule Granules are a part of the product which corresponds to the time window covered by a Data Set Record (DSR) of the LADS . Product slices are made from integer numbers of granules. See Figure2.5 and Figure2.6 in "Products and Algorithms Introduction"
High-resolution Image The high-resolution ASAR images are the Image Mode products (IMS, IMP, IMG) and the SLC Alternating Polarisation mode product (APS). See Table in the section entitled "Organisation of Products" in chapter 2.
Image A pictorial representation acquired in any wavelength of the electromagnetic spectrum. Also defined as: (1) The counterpart of an object produced by the reflection or refraction of light when focused by a lens or mirror. (2) The recorded representation (commonly as a photo-image) of an object produced by optical, electro-optical, optical mechanical, or electronic means. It is generally used when the electromagnetic radiation is emitted or reflected from a scene is not directly recorded on film. For radar, the image tones represent the radar reflectivity of the scene. ( See Radar Image )
Image Artefact - SAR SAR image artefacts can occur due to platform, sensor, and/or processing problems. Some example of artefacts are: ghosting (azimuth, range, nadir), scalloping, and Automatic Gain Control (AGC) effects. Image radiometrics and geometrics can be affected. Images can sometimes be improved by being reprocessed, though artefacts are sometimes incorrigible.
Imagette Small, high-resolution, complex image product collected in wave mode.
Imagette Power Spectrum The imagette power spectrum is the distribution of signal energy in the image over the two-dimensional frequency domain.
Image Mode (IM) Product

These products are high-resolution, narrow swath products based on data acquired at one of seven sub-swaths. Swath width between approximately 56 km (swath 7)and 100 km (swath 1)across-track. Spatial resolution of approximately 30 m (for Precision product). (see also "Organisation of Products" )

Image Mode Browse (IMB) Image

The Image Mode Browse (IMB) image product is a low-resolution product that will be produced systematically together with the Image Mode Medium-resolution product.

(see also "Organisation of Products" and "Browse Products" )

Image Mode Ellipsoid Geocoded Image (IMG) Product

The Image Mode Ellipsoid Geocoded Image (IMG) product is stand-alone Image Mode Geocoded SAR image generated in either HH or VV polarisation, using the Range/Doppler algorithm with the best available instrument corrections.

(see also "Organisation of Products" and "Level 1B Image Products" )

Image Mode Medium-Resolution Image (IMM) Product These products are medium-resolution systematically generated in the PDHS from the Level 0 data collected when the instrument is in Image Mode . This product, processed to approximately 150-m resolution, features an ENL (radiometric resolution) good enough for ice applications. (see also "Organisation of Products" and "Level 1B Image Products" )
Image Mode Precision Image (IMP) Product These are high-resolution stand-alone image products created directly from the Level 0 data. The scene size is 100 km along-track by the swath width for the swath from which the data is acquired (between 56 and 100 km wide). This stand-alone image is generated using the Range/Doppler algorithm. The processing uses up to date (at time of processing) auxiliary parameters and corrects for antenna elevation gain, and range spreading loss. (see also "Organisation of Products" and "Level 1B Image Products" )
Image Mode Single-Look Complex (IMS) Product Single-Look Complex (SLC) image data is a high-resolution, narrow swath products based on data acquired at one of seven subswaths. It is intended for SAR image quality assessment, calibration and interferometric or wind/wave applications. A small number of corrections and interpolations are performed on the data in order to allow freedom in the derivation of higher-level products. (see also "Organisation of Products" and "Level 1B Image Products" )
Input Data Gap An input data gap is defined as a contiguous block of N missing lines where the value of N has been predefined for each product.
Invariance Regions A number of range samples over which processing parameters are held constant
Inverse Fast Fourier Transform (IFFT) If the Fourier Spectrum [see Fast Fourier Transform (FFT)] of an image is known, it is possible to regenerate the original image through the application of an Inverse Fourier Transform, which is simply the mathematical reversal of the FFT.
Instrument Source Packet (ISP) The Instrument Source Packets (ISP) contain the ASAR measurement data codewords, as well as the necessary information to decode the codewords for ground processing. The source packet layout covers the structure of the Packet Header and Packet Data Field, plus the interpretation of the parameters contained within the packet. For a full description of the layout and techniques used for the reconstruction of sampled data refer to the document "ENVISAT-1 ASAR Interpretation of Source Packet Data. PO-TN-MMS-SR-0248".
Level 0 Level 0 data is reformatted, time-ordered satellite data (no overlap), in computer-compatible format. Level 0 is the lowest level product in the ENVISAT PDS. ( See Table 2.7 in section entitled "ASAR Level 0 Products" in chapter 2 for a summary of these products).
Level 1B Level 1B products are geolocated products in which data has been converted into engineering units, auxiliary data has been separated from measurements, and selected calibrations have been applied to the data. These products are the foundation from which higher level products are derived. Level 0 products are transformed into Level 1B products by application of algorithms and calibration data to form a baseline engineering product. ASAR Level 1b products may be unconsolidated, fully consolidated, or partially consolidated. ( See Table 2.39 in section entitled "Level 1B High Level Organisation of Products" in chapter 2 for a summary of these products).
Level 2 The Level 2 product is a geolocated geophysical product. The Level 1B product is transformed into one, or more, Level 2 products through higher-level processing to convert engineering units into geophysical quantities and to form a data set that is easier to interpret. For ASAR there is currently only one Level 2 product (ASA_WVW_2P), referred to as the Ocean Wave Spectra product. (For more detail concerning this product see the section entitled "Level 2 Product and Algorithms" 2.7. in chapter 2 )
Line A line of pixels follows the across-track direction, its numbering starts from one and increases from North to South
Location Annotation Data Set (LADS) The LADS provides latitude and longitude of image data for wave mode, and a table of geodetic lat/longs at various range/azimuth positions and times for other images. Used to geolocate products.
Main Product Header (MPH) The Main Product Header (MPH) is in ASCII format and contains information which is common to all ENVISAT instruments.( see "Definitions and Conventions" )
Measurement Confidence Data (MCD) This was the term used by ERS for what is now referred to as the the Product Confidence Data (PCD) found in the Specific Product Header (SPH) of the product.
Measurement Data Set (MDS) The Measurement Data Set (MDS) consist of a series of Annotated Instrument Source packets (AISPs). ( see "Definitions and Conventions" )
Medium-resolution Image A medium-resolution Image product will be available at 150 m resolution, which is specifically aimed at sea ice and oceanography applications.
Module Stepping (MS) Mode The Module Stepping Mode is used to gather data from all of the instrument's 320 Transmit/Receive Modules (TRM) automatically. This mode provides an internal health checking facility on an individual module basis. The purpose of the mode is to identify malfunctioning modules which may need to be switched off, and to identify modules to which calibration offsets are to be applied. ( See also the section entitled "ASAR Level 0 Products " and "ASAR Characterisation and Calibration" 2.11. in chapter 2 and in the section entitled "In-flight Performance Verification." 3.2.2. in chapter 3 ).
Mosaic A technique whereby multiple satellite images are digitally joined, while correcting for systematic changes in radiometry and geometry, thus creating a seamless image product.
Motion Artefact - Radar Objects in the scene that are not properly imaged because of motion in the aircraft carrying the sensor (radar).
Multi-Look Cross Correlation (MLCC)

This is a Doppler centroid frequency algorithm that estimates both the integer and fractional parts of the Doppler centroid from the SAR data. The estimator determines the absolute Doppler frequency, without aliasing, obtaining both of the parameters as a function of range. Knowledge of the beam pointing angles is not needed by the algorithm, except as a cross check.

( See the section entitled "Doppler Frequency Estimator" in chapter 2).

Multi-Look Imagery Resulting image when independent images of the same area are averaged to create a single multi-look image. Such an image has a lower resolution but the speckle has been reduced. ( See also )
Multi-Temporal Imagery A collection of images of the same area, obtained at different times.
Nadir Ambiguity A form of ghosting that appears as bright linear features with approximately constant range. They occur when signal returns from nadir are strong due to near-specular reflection from targets within a very narrow slant range distance. This results in bright tone. Due to pulse compression, the bright return is restricted to a small number of range cells. This results in the sharp, linear shape.
Near Real Time (NRT) Products There are two types of Near Real Time ( NRT ) products: those to be produced within 3 hours and those to be produced within one day.
Ocean Wave Mode see Level 2
Off-line (OFL) Products Some products will be processed off-line. The availability time depends on the complexity of the processing and the availability of auxiliary data. Delivery time ranges from two business days to four weeks.
Orbit Designator (Ascending or Descending ) A satellite in a polar orbit, such as ENVISAT, has an Ascending orbital designation when
travelling northbound and a Descending orbital designation when travelling southbound. The orbital designation of the SAR data is determined by the satellite position at the start of
the imaging activity.
Partially Consolidated Product This is a Level 1b ASAR product, that has been consolidated in all ways except that it does not use the most precise auxiliary data possible to perform processing. Since several different levels of accuracy exist for auxiliary data (e.g., 5 possible orbit state vector sources) varying levels of consolidation may exist for a product.
Pixel Picture element, the smallest display element. For a discussion on pixel spacing see FAQs(Chapter 4. ). Product pixels are a matrix of points where 1) lines (frames) correspond to the ASAR sampling instants and cope with the swath at those instants; 2) columns correspond to regular subdivisions of the interval between two adjacent columns of the tie points matrix, i.e. product columns are sampling the swath at constant distance. (See also )
Point Target

A point target is an idealized single scatterer that reflects the transmitted pulse. Used to model the SAR signal for processing.(See also the section entitled "ASAR Level 1B Algorithm Physical Justification" in chapter 2).

Precision Image Product (PRI) The Precision Image product is a multi-look, ground range, digital image (in either HH or VV polarisation) suitable for most applications. It is intended for multi-temporal analysis and for deriving backscatter coefficients. Engineering corrections and relative calibration are applied to compensate for well understood sources of system variability. Absolute calibration parameters are provided in the product annotations.

Preprocessing is applied to all raw data before the other parameter estimation and image formation steps are performed. (see "Preprocessing " section in chapter 2)

Product Confidence Data A flag that simultaneously provides surface type information (land, water or cloud), additional scientific information relevant to the product interpretation (dark vegetation, turbid waters, absorbing aerosols etc.), and confidence information for each product. ( See also "Definitions and Conventions" and "Level 1B Essential Product Confidence Data" )
Quick-look Imagery produced immediately after data reception. The imagery lacks corrections, but has sufficient resolution and clarity to provide visual information for most users.
Radar Image A Radar Image is the mapping of the observed radar reflectivity of a scene. For radars with digital image processing, the image consists of a file of digital numbers assigned to spatial positions on a grid of pixels, and presented either as hard copy (such as a photographic print) or soft copy (such as a digital data record). All radar images are subject to statistical variations, mainly speckle and noise, which must be accommodated in either visual or numerical image interpretation. The most commonly used image formats occur after detection.
Radar Processing Sometimes denoted pre-processing , it is the means of converting the received reflected signal into an image. Processing consists of image focusing through matched filter integration, detection, and multi-look summation. The output files of a SAR processor usually are presented with unity aspect ratio (so that range and azimuth image scales are the same). Images may be either in slant range or ground range projection. Both of these spatial adjustments require resampling of the image file. (The algorithms used to generate the different ASAR images are discussed in the sections entitled "ASAR Level 1B Algorithms 2.6.1. " and "ASAR Level 2 Algorithm Description" 2.7.1. in chapter 2).
Radiometric Correction This procedure corrects and calibrates the gain and offset variations in radar imagery.
Range Ambiguities Unwanted echoes that fall into the image from ranges that, in fact, are outside of the intended swath, due to the range sampling operation of the radar. Range ambiguities may be minimised by antenna pattern and imaging mode control.
Range Bin An range bin refers to a particular range sample number.
Range Cell Migration Correction (RCMC) Range Cell Migration Correction (RCMC) is the step of correcting for the changing range delay to a point target as the target passes through the antenna beam (range migration). See the discussion "Range Cell Migration Correction (RCMC)" in the section entitled "Range Doppler" in chapter 2.
Range Compression

Is matched filtering of the received echo. See the discusion "Range Compression" in the section entitled "Range Doppler" in chapter 2.

Range Dependent Gain Correction The range compressed data is multiplied by a vector that corrects the effects due to elevation beam pattern and range spreading loss.
Range Fast Fourier Transform (FFT) FFTs are performed in the range direction. For most products, this consists of two overlapped FFTs per range line. See the discusion "Range Compression" in the section entitled "Range Doppler" in chapter 2.
Range Inverse Fast Fourier Transform (IFFT) IFFTs are performed in the range direction. Again, this usually consists of two overlapped IFFTs. Each segment is inverse FFT'd to get the range compressed data. Part of each segment is thrown away since the compressed range data is shorter than the uncompressed range data by the length of the transmitted pulse. The range matched filter is designed so that the throw-away is at the end of the inverse FFTed data. The results from each segment are then joined together to get the compressed data for the whole range line. See the discusion "Range Compression" in the section entitled "Range Doppler" in chapter 2.
Range Matched (RM) Multiply The frequency domain data is multiplied with the range matched filter. Each FFT'd segment is multiplied by the frequency response of the matched filter. See the discusion "Range Compression" in the section entitled "Range Doppler" in chapter 2.
Range Multi-Looking A set of band pass filters are applied to the data to extract multiple range looks (if necessary).
Range Resolution Resolution characteristic of the range dimension, usually applied to the image domain, either in the slant range plane or in the ground range plane. Range resolution is fundamentally determined by the system bandwidth in the range channel.
Raw Data Raw data is data as received from the satellite (serial data stream, not demultiplexed). Raw data is recorded from the X and Ka band demodulator output interfaces and stored on High-Density Data Tapes (HDDTs). The Raw Data is not considered a product.
Raw Data Analysis

Complex data is collected in-phase (I) and quadrature-phase (Q) channels. Receiver electronics may introduce biases or cross-coupling (non-orthogonality) between the I and Q channels. This can be estimated by collecting statistics of the I and Q channels. These statistics are collected by accumulating the sums I, Q, I squared and Q squared . Only a fraction of the data set is used.

( See also Complex Number in the Radar and SAR glossary )

Raw Data Correction The following operations are performed for each sample: I/Q bias removal in one of the channels, power balance in one of the channels (I/Q gain imbalance correction), and phase (I/Q non-orthogonality) correction in one of the channels. ( See also Complex Number in the Radar and SAR glossary )
Regional Coverage A regional product may only cover a specific segment of an orbit.
Resolution The minimum separation between two objects of equal reflectivity that enables them to appear individually in a processed radar image. Also referred to as spatial resolution. Resolution in a radar system differs in two directions: the azimuth (or along-track direction) and the range (or across-track) direction.
Resolution Cell A two-dimensional cylindrical volume surrounding each point in the scene. The cell range depth is slant range resolution, and its width is azimuth resolution
Root Mean Squared (RMS) Equalisation The Root Mean Squared (RMS) Equalisation method is an FBAQ decoding option whereby the decoder attempts to make the RMS of the decoded data equal to that of the original signal data. This is done at the expense of mean-squared error performance (i.e. the algorithm is no longer a true optimum minimum mean square quantizer when this option is used). Note that for SAR data, characterized by a zero mean Guassian distribution, the RMS of the data is equal to the square-root of the variance. Also note that RMS Equalisation is not expected to be used operationally, but may be used for some Wave Mode experiments.
Roughness Variation of surface height within an imaged resolution cell. For radar images this term describes the average vertical relief of small-scale irregularities of the terrain surface. A surface appears rough to microwave illumination when the height variations become larger than a fraction of the radar wavelength. The fraction is qualitative, but may be shown to decrease with incidence angle.
Scalloping A corduroy-like radiometric banding across (rangeward) the scene caused by the improper estimation of the Doppler centroid. The image can be reprocessed using better Doppler centroid estimates. For a further discussion on this topic see the section entitled "Descalloping" and "Doppler Frequency Estimator" in chapter 2).
ScanSAR Beam Merging ScanSAR multi-beam processing consists of generating independent beam images, called beam buffers and subsequently combining them into a single output line. ( See the section entitled "ScanSAR Beam Merging " in chapter 2).
Scattering Coefficient The ratio of the average reflected electromagnetic wave power to the incident electromagnetic power, for distributed scattering targets.( See also Sigma Nought )
Scattering Matrix Array of four complex numbers that describe the transformation of the polarisation of a wave incident upon a reflective medium to the polarisation of the backscattered wave. It is the polarisation vector counterpart to the coefficient of reflectivity.
Shadow - Radar

A radar shadow is the absence of radar illumination because of intervening reflecting or absorbing objects. The occurrence, shape and amount of radar shadow caused by either concave or convex relief features are dependent on several factors. These include radar look direction, incidence angle and platform altitude, as well as terrain (object) configuration, slope angle and slope orientation. Shadow effects are most prominent with large incidence angle illumination; they occur in the down-range direction and may serve as a good indicator of the radar illumination direction, topography, and height. In high relief terrain, radar shadow effects may obscure a significant amount of surface area, which is most obvious in large incidence angle (e.g. >50?) airborne SAR imagery. Satellite-based radar tends to produce far less radar shadow effects, but other important aspects come into play, such as slope foreshortening and layover. There is no measurable target return signal in radar shadow (other than noise).


Radar Shadow
( See also "Elevation Displacement" in Geometry glossary.
Sigma The conventional measure of the strength of a radar signal reflected from a geometric object (natural or manufactured) such as a corner reflector. Sigma specifies the strength of reflection in terms of the geometric cross section of a conducting sphere that would give rise to the same level of reflectivity. (Units of area, such as metres squared). See also Backscatter in radar glossary.
Sigma Nought Scattering coefficient, or the conventional measure of the strength of radar signals reflected by a distributed scatterer, usually expressed in dB. It is a normalised dimensionless number, comparing the strength observed to that expected from an area of one square metre. Sigma nought is defined with respect to the nominally horizontal plane, and in general has a significant variation with incidence angle, wavelength, and polarisation, as well as with properties of the scattering surface itself. See also chapter 3 "Pre-flight Characteristics and Expected Performance" and Backscatter in radar glossary.
Sign + Magnitude Mode (S+M) The Sign + Magnitude Mode (S+M), or Fixed Exponent mode, is a data compression technique used in ASAR data processing. For a further description of this method, refer to the document "ENVISAT-1 ASAR Interpretation of Source Packet Data. PO-TN-MMS-SR-0248". ( See also Flexible Block Adaptive Quantisation (FBAQ) method ).
Single Look Complex Image (SLC) Single Look Complex (SLC) image data are intended for SAR image quality assessment, calibration and interferometric or wind/wave applications. A small number of corrections and interpolations are performed on the data in order to allow freedom in the derivation of higher level products. ( See Table 2.39 in the section entitled "Level 1B High Level Organisation of Products" )
Slant Range to Ground Range (SR/GR) Conversion Converts the distance from the radar (slant range) to distance along the ground ( ground range ) and the range resampling to a desired output pixel spacing.
Slice A slice is an integer number of granules. See Figure and Figure in "Products and Algorithms Introduction". In stripline processing, the PF-ASAR will systematically generate output parent products, within the time constraints, that cover an entire acquisition segment by processing a number of separate scenes and then joining the scenes to form the continuous segment. Most long data segments will be processed using more than one processing computer, in order to meet throughput performance requirements. Each computer will be given a portion of the input data segment to process. The output, referred to as slices, from the different computers are then concatenated to produce one long strip product, referred to as "Stripline Product" ( See also Figure2.2 in the section entitled "Products and Algorithms Introduction"in chapter 2).
Specific Product Header (SPH) The Specific Product Header (SPH) is in ASCII format and contains information which describes the specific product as a whole. It will vary between instruments and between different products for each instrument. The SPH also contains Data Set Descriptors (DSDs). DSDs are used to point to and describe the various Data Sets which make up a product. ( see also "Definitions and Conventions " )

Speckle refers to a noise-like characteristic produced by coherent systems, including synthetic aperture radars (SARs). It is evident as a random structure of picture elements (pixels) caused by the interference of electromagnetic waves scattered from surfaces or objects. When illuminated by the SAR, each target contributes backscatter energy which, along with phase and power changes, is then coherently summed for all scatterers. This summation can be either high or low, depending on constructive or destructive interference. This statistical fluctuation (variance), or uncertainty, is associated with the brightness of each pixel in SAR imagery. When transforming SAR signal data into actual imagery, multi-look processing is usually applied. The speckle still inherent in the actual SAR image data can be reduced further through processing tasks such as filtering. Unlike system noise, speckle is a real electromagnetic measurement, which is exploited in SAR interferometry.(InSAR)

( See also )

Speckle Filter A radiometric enhancement technique that reduces speckle with a minimum loss of information. Filtering permits better discrimination of scene targets and easier automatic image segmentation. In addition, after an image has been filtered, classical enhancement techniques can be applied with improved results (e.g. edge detectors, textural classifiers). In homogeneous areas, the filter should preserve radiometric information and the edges between different areas. In textured areas, the filter should preserve radiometric information, and spatial signal variability (textural information).
Stereo Imagery Two images of the same area taken from different sensor stations so as to afford stereoscopic vision.
Stokes Matrix A description of the complete polarisation signature of a reflective medium. 4x4 array of real numbers that describes the transformation of the Stokes parameters of the incident wave into the Stokes parameters of the electromagnetic wave reflected by each element of a scene illuminated by a radar.
Stokes parameters Set of four real numbers that together describe the state of polarisation of an electromagnetic wave.
Stokes Vector A four component real vector that describes the polarisation state of an electromagnetic wave in terms of combinations of the perpendicular wave components.
Stand-alone Products Also referred to as "On Request" products, these are not generated unless specifically requested by a user.The ASAR stand-alone products are: Precision, Ellipsoid Geocoded and Single Look Complex images.
Stripline Products

Stripline products are generated along a complete segment or an orbit. Geometric and radiometric continuity are ensured along the complete segment or orbit. Scenes can be ordered from anywhere within a stripline, then extracted and distributed via the PDS User Services (no framing constraint). Stripline processing of browse, medium-resolution and low-resolution data will produce products for up to 10 minutes data acquisition in Image (IM), Alternating Polarisation (AP) and Wide Swath (WS) Modes, and up to a full orbit for Global Monitoring (GM) Mode. ( See also "Products and Algorithms Introduction" in chapter 2 and "Level 1b Image Products" in chapter 2 ).

Strip Map A strip map is an image formed in width by the swath of the imager and follows the length contour of the flight line of the imager itself. Strip map images are generally not geocoded since they follow the irregular path of the imaging platform.
Sub-look Image Terms A sub-look image is one of the images formed from one of the azimuth frequency bands (looks) during cross spectra calculation.

Mean, variance, skewness, and kurtosis are statistical terms that are defined mathematically.
Say x is a sample of a sublook image. It is treated as a random variable. Let E(x) be the mean, or average of x over the image. Denoting this mean value by x', then the other statistics are defined as:
variance = E((x-x')^2)
skewness = E((x-x')^3)
kurtosis = E((x-x')^4)

Where the ()^n notation means to the n'th power'. That is x^2 is x squared.

Surface Roughness See Roughness
Summary Quality Annotation Data Set (SQADS) An ADS that contains the Summary Quality (SQ) information of a product, such as the Product Confidence Data (PCDs).
Swath The width of an imaged scene in the range dimension, measured in either ground range or slant range on the swath. See also chapter 1 "Principles of Measurement" 1.1.3. , and chapter 3 "ASAR Instrument Functionality 3.1.2. " for a further discussion on ASAR swath modes.
Synthetic Aperture Strip Map (SASM) See Strip Map
Systematic Product Products that are generated automatically for all received data as opposed to stand-alone.
Texture - Radar Texture is generally referred to as the detailed spatial pattern of variability of the average reflectivity (tone). Image texture is produced by an assembly of features that are too small to be identified individually. SAR image texture is composed of a convolution of speckle with scene texture. Texture is an important radar image interpretation element; its statistical characterisation requires measurement from a finite sampling window rather than estimates from a single picture element (pixel). Texture edge detection, or segmentation, is a critical method used for accurate radar image classification. Radar image texture is apparent at various different scale levels. Micro-scale texture is the result of more or less homogeneous, noise-like and random fluctuations of light and dark tone throughout the entire image. Meso-scale texture is produced by spatially and not randomly organised fluctuations of grey tone on the order of several resolution cells, within an otherwise homogeneous unit. Examples of descriptive terms to characterise texture include rough (coarse), smooth (fine), grainy, checkered, or speckled.
Throwaway After filtering, the output signal samples at the end of the array correspond to incomplete input pulses. These are invalid output samples that are not used in further processing.
Tie Frame A set of tie points corresponding to a given time and location of the satellite.
Tie Point Tie points for a given product are a matrix of Earth points, where1) lines (tie frames) correspond to regularly spaced (time-wise) instants tf, origin at the first frame of the product. Tie points are located at successive projections at instants tf of the (YS=0) plane in the satellite fixed frame (XS, YS, ZS); 2) the central tie point is at the swath centre, i.e. the projection on the geoid of the axis ZS; 3) tie points at a given instant are spaced at even distance (the same for all tie frames) along the swath.
Tone Tone refers to each distinguishable grey level from black to white. First order spatial average of image brightness, often defined for a region of nominally constant average reflectivity. It is proportional to the strength of radar backscatter. Relatively smooth targets, like calm water, appear as dark tones. Diffuse targets, like some vegetation, appear as intermediate tones. Man-made targets (buildings, ships) may produce bright tones, depending on their shape, orientation and/or constituent materials. Tone can be interpreted using a computer assisted density slicing technique.
Unconsolidated Product This is the ASAR Level 1B product produced in NRT using available NRT auxiliary data (i.e. may not be the most precise orbit vectors or calibration information).
Wavelength Bin An wavelength bin refers to a particular wavelength sample number.
Wave Mode Products (WV)

ASAR Wave Mode (WV) products are based on small high-resolution, complex images of ocean scenes, also called imagettes . These are processed to derive spectra of the ocean backscatter and consequently the wavelength and direction of ocean waves.

A small imagette (dimensions range between 10 km by 5 km to 5km by 5km) is acquired at regular intervals of 100 km along-track.The imagette can be positioned anywhere in an Image Mode (IM) swath.Up to two positions in a single swath or in different swaths may be specified, with acquisitions alternating between one and the other (successive imagettes will hence have a separation of 200 km between acquisitions at a given position).HH or VV polarisation may be chosen.Imagettes are converted to wave spectra for ocean monitoring. ( see also "Organisation of Products" )

Wave Mode Imagette Cross Spectra (WVS) Product

The Wave Mode Imagette Cross Spectra (WVS) product is an image power spectrum product that contains up to 400 cross spectra extracted from the SLC Imagette and Imagette Cross Spectra product (WVI).

( see also "Organisation of Products" and "Level 1B Wave Products" )

Wave Mode SLC Imagette and Imagette Cross Spectra (WVI) Product

The Wave Mode SLC Imagette and Imagette Cross Spectra (WVI) product is the basic Level 1B Wave Mode product. The product includes up to 400 single-look, complex, slant range, imagettes generated from Level 0 data and up to 400 imagette power spectra computed using the cross-spectra methodology.

( see also "Organisation of Products" and "Level 1B Wave Products" )

Wave Spectra Retrieval The wave spectra retrieval algorithms are based on minimizing, with respect to the wave spectrum, the mean square difference between the observed and the computed SAR image spectrum under certain constraints. The computed SAR image spectrum is derived using the non-linear transform with the current wave spectrum, as input. ( See the section entitled "ASAR Level 2 Algorithm 2.7.1. " for a discussion of this topic).
Wide Swath (WS) Mode product The Wide Swath Mode (WS) product is a 400 km by 400 km image. Spatial resolution of approximately 150 m by 150 m for nominal product.VV or HH polarisation.( see also "Organisation of Products" )
Wide Swath Browse (WSB) Image

The Wide Swath Browse (WSB) image product is the low-resolution product that will be produced systematically together with the WS Medium-resolution (WSM) Product.

( See also "Organisation of Products" and "Browse Products" )

Wide Swath Medium-Resolution (WSM) image product This is the standard product for ASAR Wide Swath Mode and it is systematically generated in the PDHS from Level 0 data collected when the instrument is in Wide Swath Mode using the SCANSAR technique and processed to 150-m resolution. The swath width is approximately 400 km. ( see also "Organisation of Products" and "Level 1B Image Products" )
Zero Doppler Time Zero Doppler time is the along-track (azimuth) time at which a target on the ground would have a Doppler shift of zero with respect to the satellite ( i.e. when the target was perpendicular to the flight path). Also called the closest approach azimuth time. The SAR processor locates targets in the image at the zero-Doppler azimuth time.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry