The ASAR Wave Mode : Level 1 and 2 Algorithms and Products

The philosophy underlining the Level 1 and Level 2 ASAR Wave Mode algorithms is described. The resulting products are also described including the limitations that need to be understood in order for them to be correctly interpreted. In addition, the Introduction Section contains a brief review of the history of the development of the ASAR Wave Mode products. Introduction There are 3 Wave Mode products. ASA_WVI_1P: The SLC imagettes. ASA_WVS_1P: Cross spectra of the imagettes. ASA_WVW_2P: Wave spectra. The ASA_WVI_1P product needs little explanation; it is simply a series of SLC imagettes, each 10 km x 10 km in size, which are acquired every 100 km. The imagettes are 1 look in azimuth and 1 look in range. The ASA_WVS_1P, Cross spectra and ASA_WVW_2P: Wave spectra are described more fully in the following sections. The ASAR Wave Mode story began with the publication in 1995 by Engen and Johnsen of a new technique using the cross spectra for SAR Ocean Wave Inversion (Ref. 1). The ERS Announcement of Opportunity (AO3) had supported the work leading to this result. The potential of this method was quickly recognised by ESA and the advantages it offered were discussed at a User Consultation Meeting, CEOS Wind & Wave, December 1995. At this meeting it was decided to process the Wave Mode Level 1 to SLC and to proceed with the Cross Spectra algorithm, in view of its advantages (improved spectral information, suppression of speckle and directional ambiguity potentially removed). A second user consultation meeting was organised in 1997 (CEOS Wind and Wave Workshop), where early results using ERS data from the operational level 1b processor were presented. At the workshop it was decided to initiate the development of a prototype level 2 algorithm. Finally at the 1st Envisat Wind and Wave Workshop 1999 it was decided that the Level 2 algorithm would be implemented in an operational processor.