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Conference Agenda

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Session Overview
C2: ID.10611 SMOS CAL/VAL & Soil Moisture
Tuesday, 05/Jul/2016:
4:30pm - 5:30pm

Session Chair: Massimo Menenti
Session Chair: Chang-Qing Ke
Workshop: Hydrology & Cryosphere
Location: Building 7-220#, School of Resources and Environmental Science, Wuhan University

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Oral presentation

SMOS cal/val activities in China

Weiguo Zhang1, Kerr Yann2

1National Space Science Center, Chinese Academy of Sciences, China, People's Republic of; 2Center d’Etudes Spatiales de la BIOsphere (CESBIO/CNES);

The Soil Moisture and Ocean Salinity (SMOS) mission is a joint program led by the European Space Agency (ESA) with participation of the Centre National d’Etudes Spatiales (CNES) in France and the Centro Para el Desarrollo Tecnológico Industrial (CDTI) in Spain. Its main scientific objective is to observe soil moisture over land and sea surface salinity over oceans. This project which mainly focuses es on SMOS cal/val activities in China in the framework of Dragon-3 programme is collaboration between the Chinese and European teams.

Since its launch in November 2009, SMOS observations are being perturbed by radio frequency interferences (RFIs) that jeopardize part of its scientific retrieval in certain areas of the World, especially over continental areas in Europe, South-Eastern Asia, and the Middle East. Detecting and flagging contaminated observations and contacting national authorities to localize and eliminate RFI sources emitting in the protected band present a continuous challenge. This paper describes the regulatory framework for the protection of remote sensors in the 1400–1427-MHz frequency band, the effect RFI has on SMOS data and the different approaches considered to improve the detection, cancellation, and mitigation of the RFI contamination.

The SMOS satellite is designed to provide global L-band brightness temperature observations at a resolution of ∼40 km with an equatorial repeat overpass approximately every three days. Unlike other passive microwave remote-sensing satellites that are used to give soil moisture information from observations at nonideal wavelengths, such as the Scanning Multichannel Microwave Radiometer, the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), or WindSat , SMOS is dedicated to soil moisture observation from the space at an optimal wavelength (L-band; 1.413 GHz). In addition, to circumvent the passive microwave remote-sensing requirement for a single large aperture dish antenna, SMOS uses a new satellite design that is similar to the synthetic aperture techniques used in radio astronomy (such as the Very Larger Array in New Mexico, USA), which synthesize a large antenna size using a large number of individual sensors arranged in a specific pattern. One advantage of this technique is that it provides observations for a range of incidence angles for each pixel in the swath. However, a total of 69 individual receivers are used to derive a single observation means that the knowledge of the in-flight characteristics of each receiver is critically important for the technique to work. Therefore, a postlaunch commissioning phase of several months is required for validation and calibration purposes, and vicarious calibration targets play a critical role in this process. Vicarious calibration is also shown to be important following the launch of AMSR-E (which used a traditional microwave antenna), where data distribution is delayed by several months because of physical temperature drifts (caused by solar heating and the subsequent cooling in the Earth’s shadow) of the on-board hot calibration target resulting in large errors. This problem was eventually overcome by using thermal information of the Earth’s surface from other microwave radiometers in orbit at roughly the same time. Although SMOS similarly relies on cold sky and on-board reference noise injector radiometers for its on-orbit calibrations, it is explicitly stated in the algorithm theoretical basis document that the ultimate calibration can only be obtained using vicarious methods. To achieve this, surface targets with stable, or at least predictable, radiometric conditions are required. In this paper, we describe behavior of warm load calibration target, the Taklamakan Desert in China.

Multiple years of SMOS data has been analyzed to study sensitivity and geophysical parameters distribution and their meaning for downscaling algorithms development and finer scale applications.

We get to a common idea: L band passive sensing data along with other data sources and technique measures should be further investigated to fulfill more needed requirements.

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