Enivsat Radar Altimeter Individual Echoes
Radar altimeter individual echoes are a unique dataset collected by the EnviSat RA-2. The initial work on these data was performed as part of the RAIES contract for ESA ESRIN
Since this contract, the EAPRS Lab has continued to research these unique and valuable echoes, processing them globally using a customised version of the RAIES processor built by Science Systems.
Approximately every three minutes, just over one second of EnviSat RA-2 echoes are returned to earth at full 1800Hz sampling, rather than the 18Hz data present in the standard SGDR product, see ESA RAIES webpage for additional information. These data are contained within the Level 1B products. However, they are in raw state; the onboard processing must be duplicated to transform these echoes prior to use. This task is performed using the Science Systems RAIES processor, which is also run at ESA ESRIN. Researchers can get access to these data by contacting ESA
This work has led to a clear requirement for future altimeter to have a far higher sampling rate alongtrack globally.
This image shows a sequence of EnviSat RA-2 echoes over the Congo basin. Echoes are plotted vertically and stacked horizontally to show the rapidly changing surface response. As usual over inland water, complex combinations of quasi-specular and diffuse components are evident. To illustrate the enhancement offered by the burst echoes, the short section delineated by blue vertical lines shows one second of echoes for which a burst is available.
This shows the corresponding one second of 18Hz data. Several components are evident.
This figure shows the actual burst sequence. Here, far greater detail is seen of the changing surface response. Over surfaces such as inland water and sea-ice, where multiple bright targets may contribute to the echo, the enhanced along track resolution of 1800Hz data permits far more detail to be gathered from the underlying surface.