AltiCryo: a CNES altimetry concept study for cryosphere monitoring

Amandine Guillot (CNES, France)


Frédérique Rémy (LEGOS, FRANCE); Alexandre Guérin (CNES, France); Jean-Luc Courrière (CNES, France); Anne Lifermann (CNES, France); Yves Le Roy (TAS, France)

Event: 2017 Ocean Surface Topography Science Team Meeting

Session: Science IV: 25 years of satellite altimetry for Cryosphere and Hydrology: from experimental to emerging operational applications

Presentation type: Type Oral

The cryosphere monitoring is crucial for environment and climate studies. Alongside Cryosat-2, SARAL/AltiKa, another altimetry mission, developed by CNES and ISRO, has greatly contributed in advancing cryosphere studies . From its launch in 2013 until July 2016, SARAL/AltiKa flew on the same orbit as Envisat, providing continuity of topography measurement on the historic ground track of ERS1,2 since 1992. Also, the AltiKa instrument provides active (altimeter) and passive (radiometer) measurements in Ka-band, which is valuable to understand the ice and snow properties (F. Rémy et al [1]).
The French space agency (CNES) has initiated a study to propose an altimetry concept optimized for cryosphere (sea ice and ice sheets) and based on the SARAL/AltiKa heritage including Ka-Band operation and a single antenna shared by the altimeter and the radiometer. This study has been named AltiCryo. It is highlighted that no interferometric capability is considered for the AltiCryo altimeter since a compact design is foreseen.
The first step of the study was to document users’ needs for cryosphere, based on the actual knowledge acquired with current missions (both SARAL and Cryosat) and physical measurement capabilities. The outputs are a User Requirement Document and the notes from the user meeting held in Paris in February 2017 (and co-organized with ESA). The users have pointed out several critical points for the mission: covering very high latitudes (≥88°) in order to monitor Arctic multi-year ice and West-Antarctica, the need of high spatial resolution and precision, and a bi-frequency Ka/Ku altimeter so as to improve our knowledge of the snow penetration effect and enable the snow thickness measurement over sea ice.
The second step consisted in the definition of an instrumental configuration which satisfies the scientific needs. The instrument definition includes a 2 or 3 channels radiometer (to help characterizing surface properties over ice, as well as providing wet tropospheric correction over ocean) and a Ku/Ka band altimeter, thus leading to an antenna carrying up to 5 frequencies. SAR Closed Burst and interleaved modes are proposed in Ka-Band (main band) and Ku-Band, with simultaneous transmission in the two bands. Tracking flexibility is offered since tracking can be performed either in Ku-Band (target: land ice) or in Ka-Band (target: sea surfaces). The architecture, associated performances and the mass/consumption budgets are presented.
Lastly, it is intended to compare the SAR and SARin measurement configurations regarding the impact on slope correction over land ice and off-nadir detection of leads over sea ice.
[1] Frédérique Rémy, Thomas Flament, Aurélie Michel & Denis Blumstein (2015) Envisat and SARAL/AltiKa Observations of the Antarctic Ice Sheet: A Comparison Between the Ku-band and Ka-band, Marine Geodesy, 38:sup1

Oral presentation show times:

RoomStart DateEnd Date
Symphony Ballroom IV Wed, Oct 25 2017,14:45 Wed, Oct 25 2017,15:00
Amandine Guillot