Comision Nacional De Actividades Espaciales Research Articles

A Roughness Correction for Aquarius Sea Surface Salinity Using the CONAE MicroWave Radiometer

Aquarius (AQ)/SAC-D is a joint National Aeronautics and Space Administration (NASA)/Comision Nacional de Actividades Espaciales (CONAE; Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using a L-band radiometer/scatterometer that measures ocean brightness temperature (Tb) and radar backscatter (sigma-0). The application of L-band radiometry to retrieve SSS is a difficult task; therefore, precise Tb corrections are necessary to obtain accurate measurements. One of the major error sources is the effect of ocean roughness that “warms” the ocean Tb. The baseline approach, to provide this ocean roughness correction, uses the AQ radar scatterometer measurement of ocean sigma-0 to infer the radiometric excess ocean emissivity. In contrast, this paper develops an alternate approach for the AQ ocean roughness correction using the MicroWave Radiometer (MWR) Tb measurements at Ka-band. The theoretical basis of this MWR ocean roughness correction algorithm is described, which translates these Ka-band measurements to L-band to remove the AQ Tb errors that are caused by ocean wind speed and direction. MWR ocean roughness correction results are compared with corresponding results from the AQ scatterometer method. Also, AQ SSS retrievals are presented using both sets of roughness corrections that demonstrate the relative effectiveness of the MWR and AQ scatterometer approaches.

MWR Smear Effect: A Counts-Level Empirical Correction and Possible Causes

The microwave radiometer (MWR) is a Dicke radiometer on board of the Aquarius (AQ)/SAC-D satellite. It was developed by Argentine space agency, Comision Nacional De Actividades Espaciales (CONAE), and operates at 23.8 and 36.5 GHz frequencies. After MWR initially turned on, the first brightness temperature ( $\text{T}_{\text{B}}$ ) measurements were obtained, observing an anomalous recurrent effect when analyzing land/water crossings. The effect is present for all frequencies and earth incidence angles (EIAs) and results in a smearing of $\text{T}_{\text{B}}$ observations near strong contrast radiometric scenes. This paper summarizes the main features and discoveries around this anomaly leading to a general description of the problem: coupling of sequential MWR measurements. Consequently, an empirical correction algorithm is derived and validated. Also, possible causes are investigated.

Foreword to the Special Issue on Status of Aquarius/SAC-D Mission Calibration/Validation and Retrieval Algorithms

The papers in this special section focus on the Aquarius/SAC-D observatory, a partnership between the USA Space Agency, NASA, and the Argentine Space Agency, CONAE (Comision Nacional de Actividades Espaciales). Aquarius/SAC-D observatory was launched on June 10, 2011 from Vandenberg Air Force Base, Vandenberg, CA, USA. The observatory included several instruments and two of them are related to the primary goal of the mission. The primary goal of the mission was mapping ocean surface salinity, and mission parameters (e.g., the orbit and repeat cycle) were tuned to this objective. From the NASA perspective, this was a pathfinder mission to demonstrate the technology of remote sensing of sea urface salinity from space and to provide data for understanding the role of salinity in Earth’s water cycle, and Aquarius was the primary instrument. But the mission was international in scope and also fit the needs of the Argentine plans for space applications.

CONAE Microwave Radiometer (MWR) Counts to Tb Algorithm and On-Orbit Validation

The Aquarius/SAC-D, International Earth Science Satellite Mission, is a collaboration between NASA and the Argentine Space Agency (Comision Nacional de Actividades Espaciales, CONAE) that was launched on June 10, 2011 to provide scientists with monthly global maps of sea surface salinity (SSS) to understand the Earth’s hydrological cycle and to investigate global climate change. This paper concerns the microwave radiometer (MWR), a CONAE science instrument developed to provide simultaneous and spatially collocated environmental measurements that complement the prime L-band radiometer/scatterometer sensor (Aquarius) for measuring SSS. MWR is a 3-channel (23.8-GHz H-pol and 36.5-GHz V- and H-pol) passive microwave instrument that measures the Earth’s brightness temperature (Tb). This paper describes the MWR counts to Tb algorithm (V6.0) and presents results of the on-orbit Tb validation using intersatellite radiometric calibration with the Naval Research Laboratory’s WindSat (WS) satellite radiometer. In addition, an alternative MWR counts to Tb algorithm (V7.0) is presented that normalizes the MWR Tbs to WS. This latter version (V7.0) has the advantage of removing MWR time-varying radiometric calibration biases between antenna beams and channels as verified by on-orbit comparisons with WS.

Aquarius: An Instrument to Monitor Sea Surface Salinity From Space

Aquarius is a combined passive/active L-band microwave instrument that is being developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, global water cycle, and climate. Aquarius is part of the Aquarius/Satelite de Aplicaciones Cientiflcas-D mission, which is a partnership between the U.S. (National Aeronautics and Space Administration) and Argentina (Comision Nacional de Actividades Espaciales). The primary science objective of this mission is to monitor the seasonal and interannual variation of the large-scale features of the surface salinity field in the open ocean with a spatial resolution of 150 km and a retrieval accuracy of 0.2 psu globally on a monthly basis.