Radar altimeter data quality flagging

Abstract

The Seasat radar altimeter was designed to provide precise and accurate surface height measurements over the ocean. These data have been used in studies of the ocean geoid, tides and currents. Several factors can affect the quality of the height measurements produced by the on-board processor. In particular, radar returns with time profiles which depart from a standard form can introduce significant errors. These arise over very calm seas, over rain cells or when sea ice or land are present within the altimeter footprint. Blunder point algorithms are used in the ground processing to flag outlying data points, but these fail to identify some of the anomalies that we observe. We have developed an alternative method for flagging poor quality data using a simple algorithm based on pulse shape. We demonstrate that the algorithm provides a sensitive means of editing altimeter ocean data. Furthermore changes in surface type, such as transitions between open water and sea ice can be accurately located.