Page 1 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre ASAR APP & APM Image Quality Peter Meadows & Trish Wright  Properties of APP & APM Products  Example APP & APM Products  Analysis Approach  Format Verification  Visual Inspection  Impulse Response Function Measurements  AP Cross-Polarisation Ratio  AP Channel Co-Registration  Equivalent Number of Looks and Radiometric Resolution  Azimuth Ambiguities  Localisation Accuracy  Preliminary Radiometric Calibration  Noise Equivalent Radar Cross-Section  Summary

Page 2 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Properties of APP Imagery Ground range detected alternating polarisation imagery Dual polarisation (HH & VV, HH and HV or VV & VH) Elevation antenna pattern and range spreading loss corrections applied Size up to 300Mbytes with 2 byte (16bit) amplitude pixel values Swath widths of 100 km (IS1) to 56 km (IS7) with azimuth extents of ~100 km Azimuth resolution of 27.6m (2 looks of ~250 Hz each) Range resolution from 21m (IS2 far range) to 37m (IS1 near range) and ~26m for IS3 to IS7 (1 look) 12.5m by 12.5m pixels (hence under-sampling for spatial resolutions less than 25m)

Page 3 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Properties of APM Imagery Ground range detected alternating polarisation medium resolution imagery Dual polarisation (HH & VV, HH and HV or VV & VH) Elevation antenna pattern and range spreading loss corrections applied Size up to few Mbytes with 2 byte (16bit) amplitude pixel values Swath widths of 100 km (IS1) to 56 km (IS7) with azimuth extents of ~100 km up to 4000 km Azimuth resolution of 135m (10 looks of ~50 Hz each) Range resolution from 109m (IS1 far range) to 163m (IS1 near range) and ~130m for IS3 to IS7 (1 look) 75m by 75m pixels

Page 4 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre APP & APM Products The blue orbit numbers are of The Netherlands and the purple are of Resolute, Canada. All products are processed with v3.03 No IS1 data Two APP products had saturated ASAR transponders (orbits 3812 & 3855)

Page 5 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Example APP Products 14 July 2002 IS2 HV & HH Ottawa, Canada

Page 6 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre 6 November 2002 IS2 HV & HH Resolute, Canada

Page 7 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre 6 November 2002 IS2 HV & HH The Netherlands

Page 8 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre 9 November 2002 IS3 HV & HH Example APM Products

Page 9 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre 12 November 2002 IS3 VV & VH

Page 10 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Analysis Approach Format verification using EnviView & the ESA SAR Product Control Software (developed by DLR & BAE Systems) Image analysis performed using SAR Control Software (point target & calibration modules) and following the ESA document on Quality Measurement Definitions for ASAR products Format Verification No problems identified with APP & APM format or header parameters, however many of the APP products had no Chirp Parameter ADSR (hence no annotated Chirp Powers) Visual Inspection No problems found with any post Orbit 3661 v3.03 APP or APM products

Page 11 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Impulse Response Function Measurements (APP) IRF parameters have been derived using the ESA transponders in The Netherlands and the Radarsat transponders in Canada (images 1.6 by 1.6 km). Fredericton (HH) Resolute (HH) Aalsmeer (HV)Edam (HH) Swifterbant (HV)Resolute (HV) Fredericton (HV)Edam (HV) Zwolle (VH)Edam (VV)

Page 12 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Example APP Impulse Response Functions Radarsat transponder, i = 15.81°, azimuth resolution = 27.49m, range resolution = 34.70m ASAR transponder, i = 23.85°, azimuth resolution = 27.83m, range resolution = 24.14m

Page 13 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Spatial Resolution (3dB width of IRF): Note that the IS1 swath extends to 22.2° and that the IS2 swath starts at 19.2°. Azimuth resolution (y): 28.09±1.97m (c.f. ~27.6m theoretical value, +10% limit & 30m requirement) Range resolution (x): (c.f. theoretical values, +10% limit & <38m requirement for IS1 and <30m requirement for IS2 - IS7)

Page 14 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre ±1.44dB (c.f dB theoretical value, +5dB limit & <-12dB requirement) Integrated Sidelobe Ratio (ratio of energy in the sidelobes up to a box 20x by 20y to the energy in the mainlobe(2x by 2y)): Peak Sidelobe Ratio (ratio of the intensity of the most intense peak outside the main lobe up to 10x by 10y to the energy in the mainlobe): ±0.94dB (c.f dB theoretical value, +5dB limit & <-20dB requirement) Spurious Sidelobe Ratio (ratio of the intensity of the most intense peak outside 10x by 10y up to 20x by 20y to the energy in the mainlobe): ±2.20dB (c.f. <-25dB requirement)

Page 15 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Impulse Response Function Measurements (APM) IRF parameters have been derived using the ESA transponders in The Netherlands and the Radarsat transponders in Canada (images 4.8 by 4.8km): Resolute (HH)Aalsmeer (VH)Edam (VV) Zwolle (VH)Swifterbant (VH)Resolute (HV)Aalsmeer (HV)Edam (VH) Edam (HV)Swifterbant (HV)

Page 16 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Example APM Impulse Response Functions ASAR transponder, i = 25.36°, azimuth resolution = 145.9m, range resolution = 122.1m Radarsat transponder, i = 44.22°, azimuth resolution = 144.0m (HV) & 143.7m (HH), range resolution = 132.0m (HV) & 133.9m (HH)

Page 17 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Spatial Resolution (3dB width of IRF): Azimuth resolution (y): 143.9±5.9m (c.f. ~135m theoretical value & +10% limit) Range resolution (x): (c.f. theoretical values & +10% limit) Note that the measurements are to 1/8 pixel (9.4m) and that APM products are undersampled if the resolution is < 150m.

Page 18 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre ±1.55dB (c.f dB theoretical value, +5dB limit & <-12dB requirement) Integrated Sidelobe Ratio (ratio of energy in the sidelobes up to a box 20x by 20y to the energy in the mainlobe(2x by 2y)): Peak Sidelobe Ratio (ratio of the intensity of the most intense peak outside the main lobe up to 10x by 10y to the energy in the mainlobe): ±2.57dB (c.f dB theoretical value, +5dB limit & <-20dB requirement) Spurious Sidelobe Ratio (ratio of the intensity of the most intense peak outside 10x by 10y up to 20x by 20y to the energy in the mainlobe): ±2.55dB (c.f. <-25dB requirement)

Page 19 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre AP Cross-Polarisation Ratio The ratio of the total power in the IRF of an ASAR transponder in both channels. Examples of IRF in second polarisation: Aalsmeer (HH)Edam (HV)Swifterbant (HH) Average APP cross-pol ratio (17 measurements): -32.1±4.2dB (c.f. predicted value of < -35dB). Caused by ASAR and/or transponders

Page 20 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre AP Channel Co-registration The mis-registration between the two channels computed from the difference in the location of a point target IRF peak in both channels. As the Resolute transponders give strong IRF’s in all polarisations, they have been used for the co-registration: APP products (2 measurements): 0.0m & 0.0m APM products (2 measurements): 9.4m & 0.0m

Page 21 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Equivalent Number of Looks and Radiometric Resolution Mean equivalent number of looks: 1.99±0.05 (c.f. >1.9 requirement, -10% limit) Mean radiometric resolution: 2.32±0.03dB (c.f. <2.37dB requirement) Equivalent number of looks and radiometric resolution are derived using uniform distributed targets. APP co-polarisation measurements (4 measurements): APM co-polarisation measurements (16 measurements): Mean equivalent number of looks: 56.1±16.8 (c.f. > 30 requirement, -10% limit) Mean radiometric resolution: 0.56±0.09dB (c.f. < 0.7dB requirement)

Page 22 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Azimuth Ambiguities ASAR Transponders: -27.9±2.6dB As Doppler frequencies can only be distinguished modulo the PRF, azimuth ambiguities occur within the azimuth antenna pattern sidelobes. Measurement requires either a very bright point target or a bright point target with a low ambiguity background radar cross-section. Average APP ambiguity ratio: The requirement is -25dB while the worst case prediction is ~ -27.9dB. ASAR Transponders: -28.7±1.9dB Average APM ambiguity ratio: APM Edam (VH)

Page 23 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Localisation Accuracy Mean range displacement: -3.8±26.3m Mean azimuth displacement: -12.9±60.1m Mean displacement: 57.8±30.9m The difference between the measured and predicted positions of the ASAR transponder. The predicted positions are based on image header parameters, the known location of the transponders and their time delay. The ASAR transponders have a small terrain height and hence a small range terrain displacement. APP measurements:

Page 24 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre The localisation accuracy requirement is <900m while the worst case prediction is ~75m in azimuth and between ~125m (IS1) and ~50m (IS7) in range.

Page 25 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Preliminary Radiometric Calibration The ASAR APP transponders have been used to give a preliminary radiometric calibration for swaths IS2 to IS7. As the v3.03 AP products seem to have been processed with IM nominal chirp powers, corrections have been applied to all AP radar cross-section measurements.

Page 26 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre APP K for swaths IS2 to IS4 is: 57.05±0.51dB APP K for swaths IS5 to IS7 is: 60.59±0.47dB (based on non- saturated ASAR transponders) Different K values due to different product scaling factors

Page 27 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre The derived APM calibration K is: 69.47±0.50dB (based on ASAR transponders with acceptable ISLR’s) Further measurements required before definitive calibration constants can be derived

Page 28 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Noise Equivalent Radar Cross-section NESigma0 estimated using low radar cross-section regions (ocean, open water or lakes). This gives an upper limit to NESigma0. HV APP polarisation measurements:

Page 29 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre Summary 10 v3.03 APP and APM IS2 to IS7 products analysed No format problems identified but many of the APP products had no Chirp Parameter ADSR (hence no annotated Chirp Powers) No visualisation problems found with any post Orbit 3661 v3.03 products APP azimuth & range resolutions, ISLR, PSLR & SSLR acceptable. Some range under-sampling APM Azimuth & range resolutions and ISLR acceptable. PSLR & SSLR outside expected range due to APM under-sampling in both azimuth and at almost all ground ranges Acceptable APP cross-polarisation ratio Sub-pixel AP channel co-registration

Page 30 ASAR Validation Review - ESRIN – December 2002 Advanced Technology Centre APP & APM equivalent number of looks and radiometric resolution acceptable APP & APM azimuth ambiguities acceptable APP Localisation accuracy good Preliminary calibration constants derived - more work required before definitive K values can be calculated. Noise equivalent radar cross-sections lower than predicted NESigma0