| Paper: | TU-A2.4 |
| Session: | New Concepts in Radiometry II |
| Time: | Tuesday, March 27, 11:40 - 12:00 |
| Presentation: |
Oral
|
| Topic: |
Current and future satellite missions: |
| Title: |
CRYORAD: A SPACEBORNE LOW FREQUENCY ULTRAWIDEBAND MICROWAVE RADIOMETER FOR MONITORING THE CRYOSPHERE |
| Authors: |
Giovanni Macelloni; IFAC- CNR | | |
| | Marco Brogioni; IFAC- CNR | | |
| | Francesco Montomoli; IFAC- CNR | | |
| | Marion Leduc-Leballeur; IFAC- CNR | | |
| | Giacomo De Carolis; IREA-CNR | | |
| | Francesca De Santi; IREA-CNR | | |
| | Joel Johnson; The Ohio State University | | |
| | Kenneth Jezek; The Ohio State University | | |
| Abstract: |
In the last decade L-band microwave radiometers have proven their capabilities in contributing to the monitoring of the Earth from space. Beyond their primary soil moisture and ocean salinity mission objectives, such space borne systems have revealed the possibility of investigating physical parameters of the cryosphere such as sea-ice thickness, freeze/thaw, and snow density. Recent results also demonstrate their ability to infer information on the properties of ice-sheets and ice-shelves. These studies also suggest that sensors at microwave frequencies lower than L-band could be more attractive for significantly improving observations of the geophysical variables of the cryosphere. This is because lower frequencies (i.e. longer wavelengths) penetrate more deeply. Staring from these considerations, a mission concept study (i.e. Pre Phase-0) has recently begun under the support of ASI (Italian Space Agency) to propose a space borne, low-frequency, multi-channel microwave radiometer (500MHz – 2 GHz) called CryoRad. The main objective of the mission is the monitoring and understanding of cryospheric processes in polar regions. Parameters which will be monitored with this system are: sea ice thickness (with the specific goal of investigating thicknesses 0.7 -1.2 m where current systems exhibit larger errors); ice sheet properties (in particular ice sheet temperature profiles and the presence of aquifers); ice shelf dynamics; and permafrost dynamics (freeze /thaw state; temperature profile). Secondary objectives are sea surface salinity and soil moisture. The scientific needs defined for the above mentioned topics have been translated into mission requirements, and studies have been conducted in order to define preliminary mission and instrument concept designs. The instrument design includes a 6-m reflector antenna illuminated by three feeds in order to have more on-ground adjacent footprints. Using this configuration, the instrument swath is widened, and an averaged revisit time of around 3 days is obtained for latitudes greater than 70°. Observations are performed at nadir and in circular polarization in order to avoid the problem of Faraday rotation and to improve retrieval capabilities over ice sheets. A critical point for the receiver design is the RFI mitigation strategy. Indeed, in this frequency range, the influence of RFI can obscure the thermal noise signal emitted from the Earth. In the preliminary design, IF conversion and digitization is done on the whole 500-2000 MHz bandwidth or in 2-3 sub-bands, with sub-band separation and processing performed in the digital domain. Given the mission’s polar focus, a repeating ground track with an inclination close to 90° is preferred over a sun-synchronous orbit since the latter prevents complete observation of the poles. The design study benefits from recent measurements by the NASA sponsored UWBRAD instrument, which developed an airborne version of the radiometer and performed flights in Greenland in 2016 and 2017 for ice sheet temperature retrieval. UWBRAD measurements show significant contamination by RFI, but also that processing strategies can still allow the identification of “clean” spectrum that can be used in geophysical property retrievals. Moreover, the measurements also show 500-2000 MHz emissions to provide information on ice sheet properties. These results motivate continued design studies for the Cryorad mission to enable potential submission to ESA’s recently released Earth Explorer-10 Mission Ideas call. |
