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Recommendations from CEOS CAL/VAL 2004

 

Ø Noting that the Amazon rainforest has been well studied and is currently the best natural target for SAR calibration.  Statistical evaluation of the Amazon rainforest SAR data sets acquired for more than five years shows that C and L band SAR data (ERS-2 Scatterometer data for AMI, Radarsat SAR, JERS-1 SAR) are ultimately stable with the absolute backscattering coefficients (sigma-naught or gamma-naught), which vary with frequency, polarization, and incidence angle (for sigma-naught and not for gamma-naught), and standard deviation of less than 0.3 dB, which includes diurnal and seasonal variation (CEOS SAR CAL/VAL 11th workshop report published Dec 2003).

 

Ø CEOS CAL/VAL recommends that the Amazon rainforest area be used as one of the calibration transfer standards.

 

Amazon rainforest must be regularly measured to maintain its traceability to the internationally agreed standards.

 

 

Action items:

1)     SAR subgroup to request WGISS to provide task team for Pol-In-SAR data formatting. ->In Toulouse workshop (1999), it was recommended that SLC is the only data for preserving phase for interferometry; compressed data is necessary for polarimetry. -> In Montreal (2003), two candidates were listed, SLC and the other (preserving phase).

 

In communication within science team, single Look Complex is adequate for this requirement.

(Polarimetry and interferometry)

 

2)     The WGCV SAR subgroup should set up calibration and validation reference sites (to include both natural and man made targets) :In Montreal, we have confirmed the Amazon’s stability for some test sites, 1 in Radarsat, 1 in JERS-1, and whole Amazon in ERS). Areas of the Amazonian rainforest used by ESA, JAXA and CSA are close with some overlap. Agreement to provide the coordinates of these areas was made at CEOS’04

(Radiometric and geometric calibration)

 

3)     Space Agencies should continue to improve the quality of single and full polarization SAR data by technical exchange of information on the development of SAR calibration and imaging algorithms and techniques.

 

>This action is being conducted through the several international science workshops and CEOS SAR CAL/VAL workshop.

(Polarimetry and interferometry)

 

4)     The stability of the Amazon rainforest should be systematically studied as a function of incidence angle, frequency and polarization using existing data sets including SEASAT, ERS, JERS, RADARSAT and TRMM and emerging data sets from ENVISAT, TerraSAR and RADARSAT-2. Funding to complete the study should be solicited at the CEOS Plenary.

-> (Finished).

 

One question was raised, "how does Envisat/ASAR measure the stability of the Amazon? ” Also, we should think of uploading the Amazon stability dataset (gamma-zero, sigma-zero, incidence angle, polarization) at the CEOS SAR CAL/VAL website so that any people can access. Papers for Radarsat-1, JERS-1, and ERS-1 in the Amazon session of Montreal are adequate for basic body. Adding the Envisat is hopeful.

 

(Radiometric and geometric calibration)

 

5)     Next meeting of the SAR subgroup should focus on the problem of full polarimetric SAR calibration, both establishing requirements and techniques.

 

Ø Engineering requirement has been almost (not fully) established. The scientific requirement and techniques will be discussed in future.

 

The current requirements

System stability (short and long term):0.5dB

Cross-Talk < -35 dB

Channel amplitude imbalance: 0.2 dB (soil moisture)

Channel-phase: 2°- 5°

Channel registration <0.1 pixel?

Requirements should be expressed in term of NESZ as a function of the frequency

X:            -23 dB   

C:           -25 dB   

L:            -30 dB

P:            -35 dB

(For most modes and beams this should be sufficient. However, for quad-pol and incidence angles between 20 and 25o the requirement is more stringent. For L-band -35dB)

L-band Faraday rotation correction requirement: 2.5 degree (it is accepted that C-band Faraday rotation of 2.5 is not significant)

 

(Polarimetry and interferometry)

 

6) Space agencies should ensure that calibration processes for SAR are traceable to the primary standards. -> Ongoing.

 

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry