AltimetryData flowProcessing

Altimeter measurements | Orbit Determination | Geophysical corrections | Instrumental errors | Reference surface | Flags | Retracking | High-level processing

3.2.2.6. Flags

In general, flagging consists of three parts: instrument flags (on/off), telemetry flags (preliminary flagging and editing) and data quality flags (geophysical processing flags).

• Telemetry flags are initially based on altimeter modes and concern checking of telemetry data quality. Only severely corrupted data are not processed. The flag setting used is designed to get a maximum of data into the Sensor Data Records. Science data are processed only when the altimeter is in a tracking mode.
• Quality flags involve residuals from smoothing or fits from the data themselves. Flag setting checks for gaps, exceeded limits and excessive changes. Among these flags, some have a general meaning, describing the measurement environment.
• Other flags indicate what type of surface is beneath the satellite (ocean, ice, solid earth, etc).
• Instrument flags tell us which instruments are on and/or which frequencies are used (mostly for Topex/Poseidon).

The Envisat GDR flag indicating what type of surface is beneath the satellite (0=open ocean, 1=enclosed seas and lakes, 2=continental ice, 3=land). This map is drawn using the Basic Radar Altimetry Toolbox