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Glossary

The following section briefly defines some important terms used in this document.

  1. COSP: ICEYE Customer Operations and Satellite Planning team. It handles customer operations including both standard and custom orders from receipt to fulfillment. Ensures ICEYE constellation of satellites is effectively utilized such as to best fulfill customer expectations. They also inform customers of any issues with their orders. All new customers will receive a COSP contact email during onboarding.  Customer Service can also be reached via the Contact page at ICEYE website.

  2. Data product: A deliverable set of data files.  A standard data product adheres to the specification described in this document.

  3. ESA Copernicus Contributing Mission Class: Imagery data classification based on resolution defined by the European Space Agency Copernicus Program.

  4. Ground Resolution: Refers to the smallest distance between two scatterers on the ground that can be distinguished as separate entities in the radar image. It is usually lower than the Slant Range Resolution as it is the result of projecting the SAR data captured in the slant plane into the ground plane. Its two components are:

  5. Ground Range Resolution: The ability to distinguish two objects on the ground in the range direction, which is perpendicular to the radar's flight path. It depends on the bandwidth of the radar signal and the incidence angle.

  6. Ground Azimuth Resolution: The ability to distinguish two objects on the ground in the azimuth direction, which is parallel to the radar's flight path.

  7. Incidence angle: The angle between the radar signal’s line of sight (the path from the satellite to the target) and the perpendicular (normal) to the Earth’s surface at the point where the radar beam hits the ground. 

  8. Nominal Ground Resolution: The expected ground resolution of amplitude data products resulting from SAR data acquired utilizing a specific imaging mode. This specification utilizes an incidence angle of 30 degrees to define nominal ground resolution for all imaging modes that utilize the Spotlight collection strategy. This is because, when utilizing this collection strategy, the ground resolution is typically limited by the incidence angle. This specification also provides a range of ground resolutions expected for the entire performance incidence angle range for these imaging modes. 

  9. Nominal Swath Width: The nominal swath width is the size of the image footprint in the range direction. The delivered image size in the range direction will be slightly larger than the Nominal Swath Width to ensure that the tasked area is fully covered.

  10. Nominal Swath Length: The nominal swath length is the size of the image footprint in the azimuth direction.  The delivered image length may be slightly larger than the Nominal Swath Length to ensure that the tasked area is covered. 

  11. Noise Equivalent Sigma Zero (NESZ): Noise Equivalent Sigma Zero describes the noise floor of an image. All received signals have to be stronger than the NESZ value to rise above the noise level, so it is best for NESZ to be as low as possible. The NESZ values in the imaging-mode tables are scene-centre values. Where a range is given, it is written from the best (more negative) scene-centre NESZ to the worst, across the satellites that can produce that product and across the performant incidence-angle range. The satellite-to-satellite part of that spread reflects a heterogeneous fleet: ICEYE operates satellites of several generations, flying at different orbit altitudes. In-scene NESZ variation is not specified: Spotlight scenes are small, and that variation is smaller than typical transmit-power variation.

  12. Performant Incidence Angle Range: The range of incidence angles within which the satellite's sensor can deliver optimal performance for each imaging mode. Images acquired within the performant incidence angle range are intended to meet the product specifications. 

  13. Radar Beam: Refers to the radar signal emitted from a SAR system. ICEYE satellites use electronically steered elements to control multiple radar beams. All imaging modes with the exception of the Scan and Scan Wide modes use only one beam.  Scan and Scan Wide modes use multiple beams to image different ranges (at the cost of reduced resolution).

  14. Radiometric Calibration: Radiometric calibration is the process of ensuring that the pixel values of the data products can be directly related to the power of the returned SAR signal. A calibration factor is applied to the pixel data in order to be able to calculate its mean radar cross section, which is a true measure of the radar reflectivity. All modes with the exception of the Scan and Scan Wide modes are radiometrically calibrated. While Scan and Scan Wide imagery is visually and spatially exploitable, there may be errors when converting image sample values to a mean radar cross section values.

  15. SAR Information Density (SID): SAR Information Density is the Shannon-Hartley channel capacity of the radar collection, in bits per square metre. Earlier ICEYE documents called this quantity RGIQE (Radar General Image Quality Equation), an adaptation of the General Image Quality Equation developed by NGA. SID is not the same as SIDD (Sensor Independent Derived Data), which is a file-format product in Section 5.5.1. Unlike the RNIIRS scale, which is a largely subjective assessment of image quality, SID is an objective figure of merit:

    \(i_\mathrm{im} = B_\mathrm{gr}\,B_\mathrm{az}\,\log_2(1 + \sigma_0/\mathrm{NESZ})\)

    where \(B_\mathrm{gr}\) is ground-range spatial bandwidth and \(B_\mathrm{az}\) is azimuth spatial bandwidth. The signal-to-noise term is \(\sigma_0/\mathrm{NESZ}\). NESZ is already area-normalised, so it does not change when the processor multilooks the data. Looks therefore do not appear inside the logarithm. SID scores the radar collection (the single-look information density). Multilooking is a processing choice that spends information density to reduce speckle. A higher SID value means more information is available for exploitation. The SID values in the imaging-mode tables are scene-centre values. Where a range is given, it is written from the lowest (worst) scene-centre SID to the highest (best), across the satellites that can produce that product and across the performant incidence-angle range. The satellite-to-satellite part of that spread reflects a heterogeneous fleet: ICEYE operates satellites of several generations, flying at different orbit altitudes.

  16. RMSE: The RMSE is the Root Mean Square Error of all the measured calibration points from all the satellites. In Section 2.1 there is more explanation of how ICEYE uses RMSE to express the Geospatial Accuracy of its image products. The RMSE values presented in this specification are statistical values measured across the entire ICEYE fleet.

  17. RNIIRS: Radar National Imagery Interpretability Rating Scale (RNIIRS) is a subjective scale of radar image interpretability used primarily by military analysts. The scale spans from 0 (the lowest quality:  "interpretability of the imagery is precluded by obscuration, degradation, or very poor resolution") to 10 (highest quality figure of merit). The RNIIRS values in this specification are estimates from scene-centre SID, not analyst scores of individual images. Where a range is given, it follows the same lowest-to-highest scene-centre span as SID. The satellite-to-satellite part of that spread reflects a heterogeneous fleet: ICEYE operates satellites of several generations, flying at different orbit altitudes.

  18. Slant Range Resolution:  Ability of the radar system to distinguish between two objects located at different distances along the slant range, which is the line-of-sight distance from the radar antenna to the target on the ground. Resolution of the radar image in the direction of the radar beam.

  19. Time Dominant Incidence Angle Range: The range of incidence angles within which the satellite sensor can produce an image in order to meet specific temporal or revisit requirements utilizing a specific imaging mode. This range ensures that the satellite can capture images of a target area within a specified time window, even if it means compromising slightly on image quality or resolution. Images acquired within the Time Dominant Incidence Angle Range but outside the Performant Incidence Angle Range of an imaging mode are not intended to meet the product specifications. 

  20. SIDD: Sensor Independent Derived Data is a US National Geospatial-Intelligence Agency (NGA) file format for derived SAR image products. ICEYE offers SIDD only as a custom order, bundled with SICD. See Section 5.5.1. SIDD is not SAR Information Density (SID).