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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

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Asar app apm image quality peter meadows trish wright

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


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)

Properties of APP Imagery


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

Properties of APM Imagery


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)

APP & APM Products


Example app products
Example APP Products are of Resolute, Canada. All products are processed with v3.03

14 July 2002

IS2 HV & HH

Ottawa, Canada


Asar app apm image quality peter meadows trish wright

6 November 2002 are of Resolute, Canada. All products are processed with v3.03

IS2 HV & HH

Resolute, Canada


Asar app apm image quality peter meadows trish wright

6 November 2002 are of Resolute, Canada. All products are processed with v3.03

IS2 HV & HH

The Netherlands


Example apm products
Example APM Products are of Resolute, Canada. All products are processed with v3.03

9 November

2002

IS3 HV & HH


Asar app apm image quality peter meadows trish wright

12 November 2002 IS3 VV & VH are of Resolute, Canada. All products are processed with v3.03


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

Analysis Approach

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


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).

Impulse Response Function Measurements (APP)

Aalsmeer (HV)

Edam (HH)

Edam (HV)

Fredericton (HH)

Fredericton (HV)

Swifterbant (HV)

Edam (VV)

Zwolle (VH)

Resolute (HH)

Resolute (HV)


Asar app apm image quality peter meadows trish wright

Example APP Impulse Response Functions in The Netherlands and the Radarsat transponders in Canada (images 1.6 by 1.6 km).

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


Spatial resolution 3db width of irf

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)

Spatial Resolution (3dB width of IRF):

Note that the IS1 swath extends to 22.2° and that the IS2 swath starts at 19.2°.


Asar app apm image quality peter meadows trish wright

-12.87±1.44dB (c.f. -12.4dB 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):

  • -19.07±0.94dB (c.f. -21.2dB 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):

  • -25.98±2.20dB (c.f. <-25dB requirement)


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):

Impulse Response Function Measurements (APM)

Aalsmeer (VH)

Edam (VV)

Edam (HV)

Swifterbant (HV)

Resolute (HH)

Aalsmeer (HV)

Edam (VH)

Swifterbant (VH)

Zwolle (VH)

Resolute (HV)


Asar app apm image quality peter meadows trish wright

Example APM Impulse Response Functions in The Netherlands and the Radarsat transponders in Canada (images 4.8 by 4.8km):

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)


Spatial resolution 3db width of irf1

Azimuth resolution (y): 143.9±5.9m (c.f. ~135m theoretical value & +10% limit)

Range resolution (x): (c.f. theoretical values & +10% limit)

Spatial Resolution (3dB width of IRF):

Note that the measurements are to 1/8 pixel (9.4m) and that APM products are undersampled if the resolution is < 150m.


Asar app apm image quality peter meadows trish wright

-12.37±1.55dB (c.f. -12.4dB 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):

  • -16.62±2.57dB (c.f. -21.2dB 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):

  • -21.34±2.55dB (c.f. <-25dB requirement)


Ap cross polarisation ratio
AP Cross-Polarisation Ratio <-12dB requirement)

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


Ap channel co registration
AP Channel Co-registration <-12dB requirement)

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


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

Equivalent number of looks and radiometric resolution are derived using uniform distributed targets. APP co-polarisationmeasurements (4 measurements):

APM co-polarisationmeasurements (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)


Azimuth ambiguities

ASAR Transponders: -27.9±2.6dB requirement, -10% limit)

Azimuth Ambiguities

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:

Average APM ambiguity ratio:

  • ASAR Transponders: -28.7±1.9dB

The requirement is -25dB while the worst case prediction is ~ -27.9dB.

APM Edam (VH)


Localisation accuracy

Mean range displacement: -3.8±26.3m requirement, -10% limit)

Mean azimuth displacement: -12.9±60.1m

Mean displacement: 57.8±30.9m

Localisation Accuracy

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:


Asar app apm image quality peter meadows trish wright

The localisation accuracy requirement is <900m while the worst case prediction is ~75m in azimuth and between ~125m (IS1) and ~50m (IS7) in range.


Preliminary radiometric calibration
Preliminary Radiometric Calibration worst case prediction is ~75m in azimuth and between ~125m (IS1) and ~50m (IS7) in range.

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.


Asar app apm image quality peter meadows trish wright

APP K for swaths IS2 to IS4 is: 57.05±0.51dB worst case prediction is ~75m in azimuth and between ~125m (IS1) and ~50m (IS7) in range.

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


Asar app apm image quality peter meadows trish wright

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


Noise equivalent radar cross section
Noise Equivalent Radar Cross-section ASAR transponders with acceptable ISLR’s)

NESigma0 estimated using low radar cross-section regions (ocean, open water or lakes). This gives an upper limit to NESigma0. HV APP polarisation measurements:


Summary

10 v3.03 APP and APM IS2 to IS7 products analysed ASAR transponders with acceptable ISLR’s)

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

Summary


Asar app apm image quality peter meadows trish wright

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