Abstract. The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission is one of
six high-priority candidate missions (HPCMs) under consideration by the European
Commission to enlarge the Copernicus Space Component. Together, the
high-priority candidate missions fill gaps in the measurement capability of
the existing Copernicus Space Component to address emerging and urgent user
requirements in relation to monitoring anthropogenic CO2 emissions,
polar environments, and land surfaces. The ambition is to enlarge the
Copernicus Space Component with the high-priority candidate missions in the
mid-2020s to provide enhanced continuity of services in synergy with the
next generation of the existing Copernicus Sentinel missions. CRISTAL will
carry a dual-frequency synthetic-aperture radar altimeter as its primary
payload for measuring surface height and a passive microwave radiometer to
support atmospheric corrections and surface-type classification. The
altimeter will have interferometric capabilities at Ku-band for improved
ground resolution and a second (non-interferometric) Ka-band frequency to
provide information on snow layer properties. This paper outlines the user
consultations that have supported expansion of the Copernicus Space
Component to include the high-priority candidate missions, describes the
primary and secondary objectives of the CRISTAL mission, identifies the key
contributions the CRISTAL mission will make, and presents a concept – as far
as it is already defined – for the mission payload.
This paper provides the theoretical limit for the performance of a Maximum Likelihood Estimation (MLE) DDA re-tracker for different Signicant Wave Height (SWH) conditions based on Cramer-Rao Lower Bound (CRLB) analysis.
The Poseidon-3 altimeter on board Jason-2 includes a significant new capability with respect to its predecessors, an open-loop [Détermination Immédiate d’Orbite par Doris Embarqué (DIODE)/digital elevation model (DEM)] tracker mode. This innovative mode is capable of successfully tracking the backscatter signal over rapidly varying terrains, and thus it overcomes one of the limitations of the closed-loop Poseidon-2 tracker on board Jason-1. DIODE/DEM achieves this improvement thanks to a predetermined DEM on board that, when combined with DIODE orbit ephemeris, provides improved acquisition timing and reduced data loss in the coastal zone. As a further enhancement, Jason-3 and the Sentinel-3 programs will be capable of autonomously switching to this innovative mode in selected regions. To help recommend how these missions should utilize DIODE/DEM, the authors studied the impact of the tracker mode on the accuracy and precision of wave heights and wind speed, the continuity of the sea level climate data record, and the coverage in coastal regions. The results show close agreement between the open- and closed-loop tracker modes over the open ocean with the exception of some differences at high-tidal variability areas, the coastal zone, and sea ice regions. The DIODE/DEM tracker shows better performance than the closed-loop tracker mode at the coast and in the presence of sea ice. Jason-2, when operating in open-loop mode, allows for an approximately 5% increase of successful acquisitions at the ocean-to-land transition. However, open-loop tracking exhibits more variability in regions of high tides than closed-loop.
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