| 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" 2.6.2.1.3.1.2. )
|
| 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 2.6.1.2.4. 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 2.6.1.2.4. 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" 2.6.2.1.1.2.1.6. )
|
| 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 2.6.1.2.3.
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" 2.6.2.1.1.2.1.4. )
|
| 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" 2.3.2.5.
|
| 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 2.6.1.2.2. 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" 2.6.1.2.3.1.5. 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" 2.6.1.2.3.1.3. 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" 2.6.2.1.3. ) |
| Burst Mode Products |
Image products that
are formed with the SPECAN 2.6.1.2.4. 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 2.6.1.2.4.2. 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" 2.6.1.1.3. 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 2.6.1.2.2. 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 2.3.2.5. ")
|
| 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 2.3.2.4. ") |
| 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" 2.6.1.2.4.1.4. 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" 2.6.1.2.4.2.
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" 2.6.1.2.2. . |
| 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" 2.6.2.1.3.1.4. )
|
| 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 2.6.1.2.4. 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" 2.6.2.1.3.1.1. )
|
| 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 2.6.1.2.3.
algorithm with the best available
instrument corrections.
(see also "Organisation
of Products" and "Level 1B
Image Products" 2.6.2.1.1.2.1.3. )
|
| 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" 2.6.2.1.1.3.1.1. ) |
| 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 2.6.1.2.3.
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" 2.6.2.1.1.2.1.2. ) |
| 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" 2.6.2.1.1.2.1.1. ) |
| 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" 2.3.2.2. ) |
| 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" 2.3.2.5. ) |
| 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 2.5.1.2.3.3. " 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" 2.6.1.2.2.3. 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" 2.6.1.1.4. 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 |
Preprocessing is
applied to all raw data
before the other parameter
estimation and image formation steps
are performed. (see
"Preprocessing 2.6.1.2.1. "
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" 2.3.1.4. and "Level 1B
Essential Product Confidence
Data" 2.6.2.3. ) |
| 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 2.6.1.2.1. , 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)" 2.6.1.2.3.1.4. in the section
entitled "Range Doppler" in
chapter 2. |
| Range Compression |
Is matched
filtering of the received echo. See the
discusion "Range
Compression" 2.6.1.2.3. 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" 2.6.1.2.3. 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" 2.6.1.2.3. 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" 2.6.1.2.3. 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" 2.6.1.2.4.2.
and "Doppler
Frequency
Estimator" 2.6.1.2.2. 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 2.6.1.2.4.3. " 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 2.3.2.3. " ) |
| Speckle |
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" 2.6.2.1.1.3. 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" 2.6.2.1.2.1.2. )
|
| 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" 2.6.2.1.2.1.1. )
|
| 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" 2.6.2.1.3.1.3. )
|
| 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" 2.6.2.1.1.3.1.3. )
|
| 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. |
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