Abstract's details
CryoSat/SIRAL Cal1 Calibration Orbits
CoAuthors
Event: 2016 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and retracking (SAR and LRM)
Presentation type: Type Poster
Contribution: not provided
Abstract:
The main payload of CryoSat is a Ku band pulsewidth limited radar altimeter, called SIRAL (Synthetic interferometric radar altimeter), that transmits pulses at a high pulse repetition frequency thus making the received echoes phase coherent and suitable for SAR processing. This allows to reach an along track resolution that is significantly improved with respect to traditional pulse-width limited altimeters. Due to the fact that SIRAL is a phase coherent pulse-width limited radar altimeter, a proper calibration approach has been developed. In fact, not only corrections for transfer function, gain and instrument path delay have to be computed (as in previous altimeters), but also corrections for phase (SAR/SARIn) and phase difference between the two receiving chains (SARIN only).
Recalling that CryoSat orbit has a high inclination of 92° and it is non-sun-synchronous, SIRAL temperature changes continuously along the orbit with a period of about 480 days. By analysis of the CAL1 calibration corrections, it has been verified that the internal path delay and the instrument gain variation measured on the SIRAL are affected by the thermal status of the instrument and, as a consequence, they are expected to vary along the orbit.
In order to gain knowledge on the calibration corrections (i.e. the instrument behavior) as function of latitude and temperature, it has been planned to command SIRAL in CAL1 mode continuously for a number of orbits. The analysis of the CAL1 calibration corrections produced along the Calibration orbits can be also useful to verify whether the current calibration plan is able to provide sufficiently accurate corrections for the instrument acquisitions at any latitude.
The first Cal1 calibration orbits are planned for July 2016 and required coordination among many of the mission subsystems (Mission Planning, FOS, PDS and calibration monitoring) aiming at defining a thorough strategy for the Calibration Orbits.
In this abstract, the Calibration Orbits will be presented together with the preliminary analysis of the calibration corrections generated during this activity.
Recalling that CryoSat orbit has a high inclination of 92° and it is non-sun-synchronous, SIRAL temperature changes continuously along the orbit with a period of about 480 days. By analysis of the CAL1 calibration corrections, it has been verified that the internal path delay and the instrument gain variation measured on the SIRAL are affected by the thermal status of the instrument and, as a consequence, they are expected to vary along the orbit.
In order to gain knowledge on the calibration corrections (i.e. the instrument behavior) as function of latitude and temperature, it has been planned to command SIRAL in CAL1 mode continuously for a number of orbits. The analysis of the CAL1 calibration corrections produced along the Calibration orbits can be also useful to verify whether the current calibration plan is able to provide sufficiently accurate corrections for the instrument acquisitions at any latitude.
The first Cal1 calibration orbits are planned for July 2016 and required coordination among many of the mission subsystems (Mission Planning, FOS, PDS and calibration monitoring) aiming at defining a thorough strategy for the Calibration Orbits.
In this abstract, the Calibration Orbits will be presented together with the preliminary analysis of the calibration corrections generated during this activity.