Learning from the Field of Photometry: The Way Towards Better Radiometric Measurements

Transcription

1 Chart 1 Learning rom the Field o Photometry: The Way Towards Better Radiometric Measurements Björn J. Döring, Marco Schwerdt October 8, 2013

2 Chart 2 > Vortrag > utor Dokumetname > Datum [Show image o TSX satellite]

3 Chart 3 Traceability Know Example SR What to measure Length [m] RCS [m²] How to measure it T = 20 C, C-band, 100 MHz BW Traceable uncertainty o measurement standard PTB/NIST calibration certiicate?? Corner relector, transponder

4 Chart 4 What We Measure Point target

5 Chart 5 Status Quo Calibration point targets are described by Radar Cross Section (RCS) E 2 2 r σ = lim 4πR R E 2 i Body property, depending on: - Wavelength - Incidence angle o (plane) wave - Polarization o radar transmitter and receiver - Position o transmitter and receiver (monostatic vs. bistatic)

6 Chart 6 Eects Inluencing the Point Target Impulse Response Impulse response is aected by much more than just the target RCS!

7 Chart 7 > re Pixel Intensities Proportional to RCS in SR Images? > Björn Döring > July 25, 2012 Body property Pixel intensity RCS = Ratio o powers E σ πr E Correlation o complex amplitudes ( averaging over requency and angle ) 2 2 r 2 = lim 4 R 2 Ixy (, ) = [ KSxy (, ) hxy (, )] i

8 Chart 8 Proposed New Measurement Quantity The RCS replacement The equivalent radar cross section shall be equal to the radar cross section o a perectly conducting sphere which would result in an equivalent pixel intensity i the sphere were to replace the measured target.

9 Chart 9 Equivalent Radar Cross Section (ERCS) What stays the same? - Measurement procedure: No additional correction actors necessary - Measurement unit: [m²] - Understanding: Still thinking o ratio relected/incident power What changes? - nnotation More clarity (know what you measure) - Calibration! - Reerence or absolute radiometric calibration must be given as equivalent RCS, not as RCS - Deinition works or low to highresolution SR systems

10 Chart 10 FSR P band (E)RCS o Trihedral Corners Bandwidth m MHz 50 MHz 20 MHz 300 MHz 600 MHz Frequency dependence

11 Chart 11 Midpoint Conclusions Know What to measure RCS ERCS How to measure it Traceable uncertainty o measurement standard

12 Outputs Inputs K 1 K 2 Cal. actors system 1&2 Chart 13 Calibration target I 1 I 2 Pixel int. o target I 1 I 2 Pixel int. o SR system 1 SR system 2 Target ERCS o target ERCS o Target B B B σ = I K

13 Outputs Inputs 50 % K 1 K 2 Cal. actors system 1&2 Chart 21 Calibration target 50 % I 1 I 2 Pixel int. o target 50 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target ERCS o target ERCS o Target B B B σ = I K

14 Outputs Inputs K 1 K 2 Cal. actors system 1&2 Chart 22 Calibration target I 1 I 2 Pixel int. o target I 1 I 2 Pixel int. o SR system 1 SR system 2 Target ERCS o target ERCS o Target B B B σ = I K

15 Outputs Inputs 67 % K 1 K 2 Cal. actors system 1&2 Chart 23 Calibration target 33 % 50 % I 1 I 2 Pixel int. o target 67 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target ERCS o target ERCS o Target B 50 % 50 % 50 % 50 % B B σ = I K

16 Outputs Inputs 42 % K 1 K 2 Cal. actors system 1&2 Chart % Calibration target 33 % 38 % I 1 I 2 Pixel int. o target 67 % 75 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target 80% ERCS o target ERCS o Target B 75 % 160 % 150 % 105 % 105 % B B σ = I K

17 Outputs Inputs 42 % K 1 K 2 Cal. actors system 1&2 Chart % Calibration target 33 % 38 % 67 % 75 % SR system 1 SR system 2 Target 80% Measured σ seem uncalibrated despite calibration Result o requency dependence o calibration target and I 1 SR I 2 systems I 1 I 2 Pixel int. o Pixel int. o ERCS o ERCS o target target Target B 75 % 160 % 150 % 105 % 105 % B B σ = I K

18 Outputs Inputs 67 % K 1 K 2 Cal. actors system 1&2 Chart 26 Result 1: Calibration target needs to be controlled Sphere-like target! Calibration target 33 % 50 % I 1 I 2 Pixel int. o target 67 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target 50 % ERCS o target ERCS o Target B 50 % 50 % 50 % B B σ = I K

19 Outputs Inputs 67 % K 1 K 2 Cal. actors system 1&2 Chart 31 Calibration target 58 % 83 % I 1 I 2 Pixel int. o target 17 % 33 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target 88 % ERCS o target ERCS o Target B 125 % 17 % 33 % 520 % 375 % B B σ = I K

20 Outputs Inputs 67 % K 1 K 2 Cal. actors system 1&2 Chart 32 Calibration target 58 % 83 % 17 % 33 % SR system 1 SR system 2 Target 88 % Measured σ e seem uncalibrated, despite calibration Relative measurements within one system are dierent Result I 1 I 2 o req. responses I 1 I 2 o targets and systems Pixel int. o Pixel int. o ERCS o ERCS o target target Target B 125 % 17 % 33 % 520 % 375 % B B σ = I K

21 Outputs Inputs Result 2: Frequency response (oremost apodization/weighting during processing) needs to be controlled/standardized 67 % K 1 K 2 Cal. actors system 1&2 Chart % Calibration target 58 % 58 % I 1 I 2 Pixel int. o target 17 % 17 % I 1 I 2 Pixel int. o SR system 1 SR system 2 Target ERCS o target ERCS o Target B 88 % 88 % 17 % 17 % 520 % 520 % B B σ = I K

22 Inputs Control reerence! (e.g. sphere-like target) Control system! (using standardized apodization unctions) Measure! (any requency or angular dependence allowed high-resolution systems) Outputs Chart 36 σ = I K

23 Chart 38 > Vortrag > utor Dokumetname > Datum Hipparcos eye Telescopes Daguerreotypy 200 BC 18th century Chart 38 Image: ESO/Y. Beletsky

24 Chart 39 > Vortrag > utor Dokumetname > Datum Hipparcos eye Telescopes Daguerreotypy 200 BC 18th century 1870 Open OpenCluster ClusterM103 M103on onfn J plate plate Open Cluster M103 on plate Source: Michael Richmond Chart 39 Image: ESO/Y. Beletsky

25 Chart 40 > Vortrag > utor Dokumetname > Datum Hipparcos eye Telescopes Daguerreotypy 200 BC 18th century Chart 40 Photomultiplier tubes UBV ilters RI ilters Image: ESO/Y. Beletsky

26 Chart 41 > Vortrag > utor Dokumetname > Datum Hipparcos eye Telescopes Daguerreotypy 200 BC 18th century 1870 Photomultiplier tubes UBV ilters RI ilters 1953 Source: Michael Richmond Chart Image: ESO/Y. Beletsky

27 Chart 42 > Vortrag > utor Dokumetname > Datum Hipparcos eye Telescopes Daguerreotypy 200 BC 18th century 1870 Photomultiplier tubes UBV ilters RI ilters Development o photometric systems SR community today CCD sensors UBVRcIc ilters Chart 42 Image: ESO/Y. Beletsky

28 Chart 43 Currently Used podization Functions Mission Functions # combinations z = Rg LOS/PLSR w r 1 RDRST-2 w k (β 2.4, 3.5 ) 3 Sentinel-1 w c (α 0.50, 0.75 ) 11 TerraSR-X w c (α = 0.60) 1 w r : Rectangular window w k : Kaiser window w c : General cosine window

29 Chart 44 podization Functions & Sentinel-1 Center req. Sentinel db

30 Chart 45 Conclusions Know What to measure RCS ERCS How to measure it Traceable uncertainty o measurement standard Standardized apodization unctions Target with known ERCS