Abstract
CryoSat-2 is the first satellite mission carrying a high pulse repetition frequency radar altimeter with interferometric capability on board. Across track interferometry allows the angle to the point of closest approach to be determined by combining echoes received by two antennas and knowledge of their orientation. Accurate information of the platform mispointing angles, in particular of the roll, is crucial to determine the angle of arrival in the across-track direction with sufficient accuracy. As a consequence, different methods were designed in the CryoSat-2 calibration plan in order to estimate interferometer performance along with the mission and to assess the roll’s contribution to the accuracy of the angle of arrival. In this paper, we present the comprehensive approach used in the CryoSat-2 Mission to calibrate the roll mispointing angle, combining analysis from external calibration of both man-made targets, i.e., transponder and natural targets. The roll calibration approach for CryoSat-2 is proven to guarantee that the interferometric measurements are exceeding the expected performance.
Highlights
The CryoSat-2 mission was designed to measure changes in the thickness of sea and land ice fields [1]
The theoretical angle of arrival is computed by geometry folwhere λ is the wavelength of the radar signal, 22.084 mm; B is the distance between the lowing: centres of two antennas, 1.1676 m; χ is the roll angle; and Φ (t,r) is the measured phase d0
The most likely roll bias is determined inthe theelevation followingresidual were obtained comparing CryoSat-2 Level1b products fromThe the results width of distribution
Summary
The CryoSat-2 mission was designed to measure changes in the thickness of sea and land ice fields [1]. The altimeter mounted on board the CryoSat-2 satellite, namely SAR/Interferometric Radar Altimeter (SIRAL), was designed with synthetic aperture and interferometry capabilities in order to meet those requirements. QWG (Quality Working Group) have been able to analyze the CryoSat-2 roll bias with three different strategies: (i) calibration over the Svalbard transponder [8], (ii) ocean roll campaigns, and (iii) analysis of CryoSat-2 swath data over land ice. Transponder acquisitions have been used to monitor range, datation, and interferometric phase performances since the beginning of the CryoSat-2 mission. With the ocean roll campaigns, better precision is achieved, and errors linked to the baseline orientation knowledge can be ignored It has the drawback of requiring spacecraft maneuvers, causing the suspension of science acquisitions. The swath processing method has the advantage of using science acquisitions available over large areas for assessing the roll bias, but a large amount of data over different regions and seasons is required
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