This readme file gives information on the content and format of the 2nd version of the files containing the RDSAR (or Pseudo LRM) data files provided by TU Delft in the frame of the CP4O project. The files are in netcdf format. There is one file per pass, combining all SAR bits along that pass, both ocean and land. The retracking was done as Remko Scharroo presented during the Living Planet Symposium in Edinburgh, using Jensen’s suggested zero-padding of the waveform, but not doing the waveform averaging that was presented there. So this should give a clean comparison with the CPP data. You will see in each file both 1-Hz data and 20-Hz data, more or less like you’re used to from the netCDF Jason products. The geophysical corrections are all 1-Hz, the measurements (corrected for instrumental drift and biases) are given both at 20-Hz and 1-Hz. There are two sets of the same data, one with the waveforms included, one without. Except for the waveform_20hz and wvf_ind fields, there is no difference between those data sets. In order to keep the files a bit manageable for those who are not interested in the waveforms I have uploaded both sets. The data is produced as per the RADS standards. All that’s different from the Jason products is: - Different variable names and attributes like scale and offset, but should be obvious given the description in the attributes. - Ocean tide DOES NOT include the load tide, so you will have to apply both. This is for historical reasons, and because it makes a more logical division between land and ocean. - The MOG2D correction is the TOTAL DAC, not just the high-frequency part, as the division between high and low is totally arbitrary and suits no scientific purpose. What is also handy, and did not appear before in the older RADS products is “ssha” (and “ssha_20hz”). These are the 1-Hz (and 20-Hz) SSHA after all corrections and editing are applied. Changes from the previous version of these files are described below: Three further (20 hz) variables have been added to these data: range_tracker_20hz_ku, waveform_scale_20hz, agc_20hz_ku -range_tracker_20hz_ku: The range according to the tracker, including all instrumental corrections, as well as Doppler and USO drift. -waveform_scale_20hz: This is a scale factor similar to the one provided in the LRM level 1B products. In the L1B products, it's an awkward combination of a scalar and an exponent (A and B) to give Watts of received power. I took a simpler approach by dividing this received power value by the transmitted power and converted that to dB. Then 151.125 was added to represent the losses at nominal altitude and zero off-nadir pointing. This makes it easy to linearly add this to the power losses due to varying altitude, attitude, atmosphere, etc. sigma0 should then be determined by adding (in dB): sigma0 = waveform_scale + retracker amplitude + attenuation because of earth curvature + attenuation because of non-nominal altitude + attenuation because of off-nadir pointing + attenuation because of SWH -agc_20hz_ku: AGC setting (corrected for the numerous errors made representing this value). It is NOT corrected for drift. It is part of the waveform_scale value, so it is NOT used IN ADDITION TO the waveform_scale_20hz. The only other things that have changed are: - ref_frame_offset (changed from -704 to -698 mm) - ssha and ssha_20hz (decreased equivalently by 6 mm) This to bring them in line with the RADS LRM data that uses the same offset of -698 mm. For any further questions, please contact remko.scharroo@eumetsat.int