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IMAGING COLLECTION CHARACTERISTICS

The following provides additional technical information on the performance of the current imaging modes used by the ICEYE fleet. Our satellites are constantly being improved with recent satellites usually having better performance. In order to manage expectations we have decided to provide the worst case values across the fleet. Some parameters warrant a more detailed explanation which you can read in the Notes section.

Table 2 provides parameters associated with ICEYE complex images and Table 3 provides the technical parameters associated with ICEYE Amplitude Images.

Technical Overview

Parameter Strip Spot Spot Extended Area Scan Comments
Product Short Name 'SM' 'SLH' 'SLEA' 'SC' Note 1
Radar Beams Used 1 1 1 4 Note 2
Nominal swath width [km] 30 5 15 100 Note 3
Nominal product length (Azimuth Direction) [km] 50 5 15 100 Note 4
Nominal collection duration [sec] 10 10 20 15
Maximum collection duration [sec] 35-72 N/A N/A 15 Note 5
Maximum Scene Length [km] 240-500 5 15 300 Note 5
Noise Equivalent Sigma-Zero [ dBm2/m2 ] -21.5 to -20 -18 to -15 -18 to -15 -22.2 to -21.5 Note 6
Azimuth Ambiguity Ratio [dB] -17 -17 -17 -17
Range Ambiguity Ratio [dB] -20 -20 -20 -20
Geospatial Accuracy [m CEP90] 9 9 9 15
ESA Copernicus Contributing Mission (CCM) Class1 VHR2 VHR1 VHR1 HR1
Polarization VV VV VV VV
RNIIRS 3.6 5.5 5.5 2.1 Note 8
RGIQE [bits/m2] 0.8 22 ? 0.1 Note 9
Performant Incidence Range [deg] 15-30 20-35 20-35 21-29 Note 12
Time Dominant Incidence Range [deg] 11-43 11-56 11-56 N/A Note 13
Table 1 : ICEYE Collections Technical Summary

Complex Image Parameters

Parameter Strip Spot Comments
Focusing plane Slant Plane
Slant range resolution [m] 0.5 to 2.5 0.5 Note 7
Slant azimuth resolution [m] 3 0.25
Impulse response weighing function (peak side level) Uniform (-13.3dB) Uniform (-13.3dB)
Slant Range Sample Spacing [m] 0.4 to 2.4 0.4 Note 7
Slant Azimuth Sample Spacing [m] 1.6 0.2
Slant range product format HDF5 + XML HDF5 + XML
SLC Product Size [GB] 3.4 to 2.9 0.6 to 7.2
Dynamic Range (bits per pixel) 32 32 Note 10
Table 2 : Parameters for ICEYE Complex Images

Amplitude Image Parameters

Parameter Strip Spot Scan Comments
Ground Range Resolution [m] 3 1 < 15
Ground Azimuth Resolution [m] 3 1 < 15
Impulse response weighing function (peak side level) Taylor Weighting (-20dB) Taylor Weighting (-20dB) Taylor Weighting (-20dB)
Ground Range Sample Spacing [m] 2.5 0.5 6
Ground Azimuth Sample Spacing [m] 2.5 0.5 6
Range Looks 1 1 to 2 1
Azimuth Looks 1 to 2 1 to 4 1
Product format Geotiff + XML Geotiff + XML Geotiff + XML
GRD Product Size [MB] 700 250, 2250 800
Dynamic Range (bits per pixel) 16 16 16 Note 11
Table 3 : Parameters for ICEYE Amplitude Images

Notes and Explanations

  1. Short Name: For example, Strip mode has 'SM' : ICEYE_X7_GRD_SM_36535_20201020T175609
  2. Radar Beams: The current generation of ICEYE satellites use electronically steered elements to control multiple radar beams. Usually this is only one beam but Scan products use multiple beams to image different ranges (at the cost of reduced resolution)
  3. Nominal Swath Width: The actual image size will be slightly larger than this to guarantee that the tasked area is covered.
  4. Nominal Swath Length: The actual image length may be slightly larger to guarantee that the tasked area is covered. The maximum value can vary from satellite to satellite due to power/data/thermal limitations.
  5. Maximum Collection Duration/Length: Spot images do not have a maximum collection duration as they image for the required amount of time to obtain a tasked azimuth resolution. For Strip and Scan modes the maximum collection duration (and therefore the maximum image length) is limited by the amount of on-board memory storage or satellite thermal limitations. As different incidence angles have different slant range resolutions in order to provide the same ground range resolution, then the maximum collection duration is also a function of incidence angle.
  6. NESZ: The noise equivalent sigma zero values are taken at scene center for near and far range extents.
  7. Slant Range Resolution: For Strip mode the transmitted bandwidth is varied to make sure that the resolution on the ground remains the same. For Spot mode the maximum bandwidth is transmitted at all times.
  8. RNIIRS: Radar National Imagery Interpretability Rating Scale is a subjective assessment of Radar Image Quality used primarily by military analysts. The scale is from 0 ("interpretability of the imagery is precluded by obscuration, degradation, or very poor resolution") to the highest quality figure of merit, 10 \cite{rniirs}.

  9. RGIQE: This is the Radar General Image Quality Equation. It is an adaptation of the concept of a General Image Quality Equation \cite{leachtenauer1997general} Developed by NGA . Unlike the RNIIRS scale which is a largely subjective assessment of image quality, the RGIQE uses maximum channel capacity (measured in bits of information) as a figure of merit. From the Shannon-Hartley Theorem \cite{shannon1984communication} the maximum information that can be carried in a signal (conventionally called a channel due to the origins in communications) is given by :

    \[ C = B \log_2\left(1+\frac{S}{N}\right) \]

    Where \(C\) is measured in bits per second, \(B\) is the bandwidth of the system and \(\frac{S}{N}\) is the signal to noise ratio. Recognising that a resolution cell in a SAR image is ultimately defined in range by the transmitted bandwidth and in azimuth by the Doppler bandwidth, a measure of the maximum information content of a resolution cell in bits/\(m^2\) can be formulated :

    \[ I = B_{az} B_{R_{ground}} \log_2\left(1 + \frac{S}{N}\right) \]

    Where \(I\) is the information content measured in bits/\(m^2\), \(B_{az}\) is the Doppler bandwidth used to form the azimuth extent of a pixel and \(B_{R_{ground}}\) is the range bandwidth in the ground plane used to form the range extent of a pixel. The noise in this case is made up from all the noise elements that contribute to reduced image quality in the final image (Thermal noise, quantization noise, sidelobes, ambiguities). In this scale the higher the figure then the more 'information' is available for exploitation within the pixel.

  10. Complex Dynamic Range: A complex number with 16bit I and 16bit Q values

  11. Amplitude Dynamic Range: Stored as an unsigned 16 bit integer.
  12. Performant Incidence Range: This is the nominal or standard range of incidence angles that the ICEYE Fleet operates over. The parameters in these tables are correct within this range of angles.
  13. Time Dominant Incidence Range: Being quite small and agile, and having an electronically steered antenna, ICEYE satellites can collect radar imagery from a wide range of angles. Outside of the Performant Incidence Range, SAR image quality may be degraded. However in some situations it may be more important to obtain a SAR image quickly rather than wait for an opportunity to image the location with the performant range of angles. For this reason ICEYE offers time dominant tasking as either a Tactical or a Custom order.

References

  1. V. Amans B. Hoersch. Copernicus Space Component Data Access Portfolio: Data Warehouse 2014 - 2020. resolution classes for EO SAR Image products. ESRIN, ESA, Via Galileo Galilei Casella Postale 64 00044 Frascati Italy, March 2015. https://spacedata.copernicus.eu/documents/20126/0/DAP_Release_Phase_2_1.0_final.pdf. ↩