across track

The direction on the ground perpendicular to the satellite path.

along track

The direction on the ground of the satellite path.

Annotation Data Set

A data set that contains data other than instrument measurements.

auxiliary 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.

Browse product

Browse products are produced for AATSR, ASAR and MERIS. They 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 generated systematically and contains image lines derived from a data segment (up to a full orbit of data).

column

A column of pixels follows the along track direction, its numbering starts from one and increases from East to West.

Data Set

A collection (one or more) of data set records in mixed binary/ASCII format.

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.

frame

The set of product pixels corresponding to a given satellite position

full resolution

The full resolution grid has 4x4 more points than the reduced resolution grid, in the across track direction it has 4481 points.

pixel geometry

A set of angles (Sun zenith angle, viewing zenith angle and azimuth difference angle) specifying how the pixel is seen from the instrument and from the Sun.

level 0 data

Level 0 is the lowest level product in the ENVISAT PDS. Raw data is retrieved from the instrument data stream that holds measurements in numerical counts.

level 1b data

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."

level 2 data

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.

line

A line of pixels follows the across track direction, its numbering starts from one and increases from North to South

location

Coordinates (geodetic latitude, longitude) of a point on the geoid, expressed in the Earth-fixed coordinate system.

low resolution

The low resolution grid has 4x4 less points than the reduced resolution grid.

Main Product Header (MPH)

The Main Product Header is in ASCII format and contains information which is common to all ENVISAT instruments.

Measurement Data Set (MDS)

The Measurement Data Set consist of a series of Annotated Instrument Source Packets (AISPs).

MERIS frame

A set of simultaneously acquired MERIS measurements; by extension the time when that set is acquired. The actual MERIS pixels are located at the known lines of sight of the MERIS pixel centres at the MERIS sampling instants. These are characterised by a pointing angle yk,m and an along-track offset from the (YS=0) plane, noted dqk,m. Considering the small variability of the along-track sampling distance along the orbit that offset is taken to be directly expressed in frames. As MERIS sensor elements have a nearly even angular spacing, the distance between their projections on Earth increases from centre to end of frame.

MERIS swath

Projection on the geoid of the sector between the extreme look directions of MERIS in the (YS=0) plane, at a given time.

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.

product pixel

Product pixels are a matrix of points where 1) lines (frames) correspond to the MERIS 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.

product swath

The arc on the geoid between the two extreme product pixels at a given time. The product swath is wider than the widest possible MERIS swath.

raw data

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.

reduced resolution

The reduced resolution grid has 4x4 less points than the full resolution grid.

scene

A square, full resolution MERIS image containing 4481 x 4481 pixels.

Specific Product Header (SPH)

The SPH is in ASCII format and contains information which describes the specific product as a whole. It varies 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.

swath angle

An angle sub-tending the arc between swath centre and a point on the swath.

swath width

The distance between the two extreme pixels (Eastern and Western most pixels) of the same frame.

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, where 1) 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.

unconsolidated

This is the Level 1b product produced in NRT using available NRT auxiliary data (i.e. may not be the most precise orbit vectors or calibration information).