Spotlight In SAR Simulation BRANDON RANDOLPH Spotlight SAR
Spotlight In. SAR Simulation BRANDON RANDOLPH
Spotlight SAR In Spotlight mode, the antenna beam is steered to continuously illuminate a desired swath throughout the flight path of the platform. The central point in the scene is referred to as the motion compensation point (MCP) or scene center.
Spotlight SAR Processing of spotlight data can be a challenge due to range rates varying over the synthetic aperture length, this effect is seen as scatterer motion through resolution cells (MTRC). [1] Since platform is focused on the scene, squint-mode operation is necessary. Utilizing polar format helps to partially mitigate MTRC and allows the range migration algorithm to remove the effect of MTRC.
Polar Format Algorithm (PFA) / Polar Reformatting Algorithm The Polar Format Algorithm is used to compensate for motion through resolution cells (MTRC) by interpolation/correction in range and azimuth. Unique to spotlight SAR. Utilized due to the discrepancy of the data being captured in a polar/spherical geometry and processing is more efficient in the cartesian format. Process of the algorithm includes taking the polar data into the Fourier domain, interpolation to a cartesian domain, and taken back into temporal.
Comparison between Cartesian and Polar Processing Left: Received Spotlight SAR data processed using Cartesian [1] Right: Received Spotlight SAR data processed using Polar/PFA [1]
ICEYE Constellation ICEYE is a Finnish satellite manufacturer that offers commercial access to its SAR imagery. Currently, ICEYE has 10 satellites in orbital constellation. These are named ICEYE-X 1 through ICEYE-X 10. Each of the ICEYE satellites are X-band radars (Carrier 9. 65 GHz) with an active phased array antenna and electronic beam steering. Ground Track Repeat time 18 -22 days
ICEYE Spotlight Parameters [4] ICEYE Parameter Spotlight Nominal Altitude 560 to 580 [km] Nominal Swath Width 5 [km] Nominal Azimuth Length 5 [km] Pulse Bandwidth 300 [MHz] Polarization / PRF VV / 2 -10 [k. Hz] Performant Incidence Range 20 – 35 [deg] Time Dominant Incidence Range 11 – 56 [deg] Slant Range (Ground) Resolution 0. 5 (1) [m] Slant Azimuth (Ground) Resolution 0. 25 (1) [m] Slant Range Sample Spacing 0. 4 [m] Slant Azimuth Sample Spacing 0. 2 [m]
ICEYE Spotlight Image Spotlight image over the airport of Atlanta on March 24 th 2020 from the ICEYE constellation. [5]
Things to do Finalize spotlight sar point target simulation and extend to some realistic scene Simulate In. SAR system with the ICEYE constellation parameters Look into the free data products of the ICEYE platform to see if there is any analysis on complex data that can be done.
Sources [1] Carrara, W. , Goodman, R. , S. AND Majewski, Spotlight synthetic aperture radar [2] Jakowats, C. , Wahl, D. , Eichel, P. , Spotlight-Mode Synthetic Aperture Radar: A Signal Processing Approach [3] Doerry A. , Basics of Polar-Format Algorithm for Processing Synthetic Aperture Radar Images. 2012 [4] ICEYE, “Iceye data product guide, ” Tech. Rep. Issue 4. 0, ICEYE, 9 Feb 2021 [5] Ignatenko V. , Laurila P. , Radius A. , et al. ICEYE Microsatellite SAR Constellation Status Update: Evaluation of First Commercial Imaging Modes (2020)
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