Altimeter Sea Ice Workshop

• Main Author: Hawkins, Jeffrey D.
• Other Authors: NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
• Format: Text
• Language: English
• Published: 1990
• Subjects: Flight Control and Instrumentation; Snow; Ice and Permafrost; *SYMPOSIA; WORKSHOPS; PE63704N; WUDN294462; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA229396; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA229396

NOARL's Remote Sensing Branch successfully carried out a demonstration program aimed at extracting sea ice formation from the Geosat altimeter signal. This effort significantly enhanced earlier limited studies done with the GOES-3 altimeter by incorporating the Automated Gain Control (AGC) and the Voltage Proportional to Attitude (VATT) parameters carried in the real- time data stream. These measures of the return pulse were combined in a ratio form to create an 'ice index,' so that all values less than a cutoff magnitude were characteristics of open water, while all remaining values above were sea ice. The altimeter footprint varies in size, depending on the surface roughness. In extremely smooth cases, the surface area in less than 1 km; in rough examples, it may be 5-7 km in areal extent. So, unless the altimeter footprint is fortuitously sampling a location where only one surface type is present (open water, first-year FY ice, multiyear MY ice, etc.), the altimeter waveform will be a mixture of returns from two or more surface types. In general, excellent results were achieved. Sea ice concentrations by ice type over the experiment area agreed with the surface truth to within 5%. When Fy and MY ice types were combined to give total ice concentration, the agreement was within 2%. Thus, linear unmixing has been shown to be a useful paradigm for extracing ice information from waveform shapes. However, this approach needs further investigation. In particular, the method of choosing end members. (i.e., the mixing polytope) in this effort was subjective. (TTL)