Ancillary data: a classical definition is 'All on-board data, other than observation and HKTM data, necessary for the product processing'. This would include in particular not only various parameters and settings but also satellite data such as OBT and time correlations if needed, navigation data, etc.
Annotation data: a data set containing data other than instrument measurements and ancillary data, for instance pixel quality data and ECMWF data derived from Level-1 processing.
Auxiliary data: data necessary to some steps of the product processing that are either provided by internal databases and/or facilities of the PDGS (e.g. the parameters, the calibration and the static data bases), or by external entities to the SENTINEL-3 system (e.g. meteorological data).
Coastal zone: sea surface extending from the coast up to 300 km offshore
(Direct) geolocation function: function that maps a point (k,j) (possibly non-integers) in an image to a point (x,y,z) on the ellipsoid surface. It is subtended by a model of the line of sight coming from point (k,j).
(Direct) ortho-rectified geolocation function: function that maps a point (k,j) (possibly non-integers) in an image to a point (x,y) on the Earth's surface, by taking into account a Digital Elevation Model (DEM) z = DEM(x,y). Theoretically (x,y,z) is the intersection of the line of sight coming from (k,j) with the Earth surface modelled as a DEM on top of a reference ellipsoid. The terrain point location is corrected from the relief effect, compared to the one computed with the direct geolocation function.
Earth surface: the Earth surface is modelled as a Digital Elevation Model (GETASSE30 provided as CFI) on top of the WGS84 ellipsoid model.
Frame: the set of measurements acquired by the OLCI instrument at a given time
Image grid : the image grid contains the radiometric values and the precise latitude/longitude/altitude for each pixel at the channel resolution (0.5 km or 1 km).
Image sample/pixel: pixel stands for Picture Element. Each pixel is a measure of radiance generally gridded, with coordinates (k,j) in an image. k indexes the rows, j indexes the columns.
Image scan: a line of pixels in the SLST Level-1B product. Note that in the Level-1C product an image scan and an instrument scan should refer to the same thing.
Infra-red (IR) radiation: electromagnetic radiation of wavelengths between about 0.75 µm and 15 µm. This is broken down into four wavelength regions:
Near-IR: 0.75-1.4 µm (OLCI Oa12 to Oa21, SLSTR S3 and S4 channels)
Short-Wave IR: 1.4-3 µm (SLSTR S5 and S6 channels)
Medium-Wave IR: 3.8 µm (SLSTR S7 and F1 cannels)
Long-Wave IR: 8-15 µm (SLSTR S8, S9 and F2 channels).
Instrument sample / instrument pixel / acquired pixel: (all equivalent terms). Pixels really acquired by an instrument, before any geometric transformation.
Instrument scan or scan trace: the trace of a single SLSTR detector element on the ground. Thus for example in the thermal channels each detector has two elements, and so a single scan will give two scan traces, displaced by 1 km in the along track direction. Adjacent scan traces represent adjacent 'rows' of the instrument grid.
Inter-channel spatial co-registration , simply referred to here as co-registration or misregistration: The definition is: maximum equivalent ground distance between the positions of all pairs of spatial samples acquired in two spectral channels and related to the same target on Earth.
Inverse geolocation function: the inverse function of the direct geolocation function.
Inverse ortho-rectified geolocation function: the inverse function of the direct ortho-rectified geolocation function.
Measurement Grid (or Instrument Reference Grid): The instrument grid is the native grid on which the SLSTR collects data as it scans. A scan number identifies the number of the scan line, starting at the Ascending Crossing Node (ANX) – the point at which the satellite crosses the Equator from South to North), while a pixel number identifies the pixel count of any scan. A detector number then maps, for each pixel, the row and the column number (aligned with the Along Track (AL) and Across Track (AC) directions) onto a two-dimensional matrix of detectors. The image grid is aligned with the sub-satellite track.
(Mis-)Knowledge error: residual error when all known corrections have been applied. The true value is given by adding the (unknown) (mis-)knowledge error to the restituted value.
NEΔT: Noise-Equivalent Temperature Difference. The sensitivity of a Thermal Infrared (TIR) sensor in resolving a temperature signal compared to the background noise.
Orbital revolution number: this number identifies the SENTINEL-3 orbit within the orbital cycle. There are 385 orbits per cycle, so the orbital revolution number is between 0 and 384.
Orphan pixels or removed pixels: These are pixels acquired by the instruments but not retained in the Level-1B gridded image, due to the Level-1B (nearest neighbour) projection on the product grid. For OLCI those pixels mainly come from overlapping areas between adjacent camera modules. For SLSTR they may come from a possible oversampled acquisition at nadir of the nadir-view, with respect to the Level-1B image gridding. In oblique view there are many orphans due to scan-to-scan along track overlap. To answer the Level-1C requirements, all those pixels are retained in Level-1B products but not gridded. Note: The expression 'orphan pixel' is used in SLSTR documents while 'removed pixel' is used in OLCI documents. The term 'ungridded pixels' is also used instead of orphan or removed pixels in this document.
Product data: any data produced by ground segment processing.
Restituted value: value retrieved when all known corrections have been applied.
Scan: a scan is defined as a complete rotation of the SLSTR scan mirrors.
Solar channels: channels with centre wavelength lower than 3.0 µm (SLSTR S1 to S6 and all OLCI channels).
Thermal channels: channels with centre wavelength larger than 3.0 µm (SLSTR S7 to S9 and F1, F2).
Visible radiation: electromagnetic radiation detectable by the human eye with a wavelength between approximately 400 nm and 700 nm (OLCI Oa1 to Oa11 and SLSTR S1 and S2 channels).