The Aquarius Ocean Salinity Mission High Stability L-band Radiometer

The NASA Earth Science System Pathfinder (ESSP) mission Aquarius, will measure global ocean surface salinity with approx.120 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand). This requires an L-band low-noise radiometer with the long-term calibration stability of less than or equal to 0.15 K over 7 days. The instrument utilizes a push-broom configuration which makes it impractical to use a traditional warm load and cold plate in front of the feedhorns. Therefore, to achieve the necessary performance Aquarius utilizes a Dicke radiometer with noise injection to perform a warm - hot calibration. The radiometer sequence between antenna, Dicke load, and noise diode has been optimized to maximize antenna observations and therefore minimize NEDT. This is possible due the ability to thermally control the radiometer electronics and front-end components to 0.1 Crms over 7 days

Aquarius Radiometer Performance: Early On-Orbit Calibration and Results

The Aquarius/SAC-D observatory was launched into a 657-km altitude, 6-PM ascending node, sun-synchronous polar orbit from Vandenberg, California, USA on June 10, 2011. The Aquarius instrument was commissioned two months after launch and began operating in mission mode August 25. The Aquarius radiometer meets all engineering requirements, exhibited initial calibration biases within expected error bars, and continues to operate well. A review of the instrument design, discussion of early on-orbit performance and calibration assessment, and investigation of an on-going calibration drift are summarized in this abstract

Aquarius and the Aquarius/SAC-D Mission

Aquarius is a combination L-band radiometer and scatterometer designed to map the salinity field at the ocean surface from space. It will be flown on the Aquarius/SAC-D mission, a partnership between the USA space agency (NASA) and Argentine space agency (CONAE). The mission is composed of two parts: (a) The Aquarius instrument being developed as part of NASA.s Earth System Science Pathfinder (ESSP) program; and (b) SAC-D the fourth spacecraft service platform in the CONAE Satellite de Aplicaciones Cientificas (SAC) program. The primary focus of the mission is to monitor the seasonal and interannual variations of the salinity field in the open ocean. The mission also meets the needs of the Argentine space program for monitoring the environment and for hazard detection and includes several instruments related to these goals

Aquarius and Remote Sensing of Sea Surface Salinity from Space

Aquarius is an L-band radiometer and scatterometer instrument combination designed to map the salinity field at the surface of the ocean from space. The instrument is designed to provide global salinity maps on a monthly basis with a spatial resolution of 150 km and an accuracy of 0.2 psu. The science objective is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean. This data will promote understanding of ocean circulation and its role in the global water cycle and climate

A Roughness Correction for Aquarius Ocean Brightness Temperature Using the CONAE MicroWave Radiometer

Aquarius/SAC-D is a joint NASA/CONAE (Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using an L-band radiometer that measures ocean brightness temperature (Tb). The application of L-band radiometry to retrieve SSS is a difficult task, and 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 Aquarius (AQ) instrument (L-band radiometer/scatterometer) baseline approach uses the radar scatterometer to provide this ocean roughness correction, through the correlation of radar backscatter with the excess ocean emissivity. In contrast, this dissertation develops an ocean roughness correction for AQ measurements using the MicroWave Radiometer (MWR) instrument Tb measurements at Ka-band to remove the errors that are caused by ocean wind speed and direction. The new ocean emissivity radiative transfer model was tuned using one year (2012) of on-orbit combined data from the MWR and the AQ instruments that are collocated in space and time. The roughness correction in this paper is a theoretical Radiative Transfer Model (RTM) driven by numerical weather forecast model surface winds, combined with ancillary satellite data from WindSat and SSMIS, and environmental parameters from NCEP. This RTM provides an alternative approach for estimating the scatterometer-derived roughness correction, which is independent. The theoretical basis of the algorithm is described and results are compared with the AQ baseline scatterometer method. Also results are presented for a comparison of AQ SSS retrievals using both roughness corrections

Microwave Radiometer (MWR) Evaluation of Multi-Beam Satellite Antenna Boresight Pointing Using Land-Water Crossings, for the Aquarius/SAC-D Mission

This research concerns the CONAE Microwave Radiometer (MWR), on board the Aquarius/SAC-D platform. MWR\u27s main purpose is to provide measurements that are simultaneous and spatially collocated with those of NASA\u27s Aquarius radiometer/scatterometer. For this reason, knowledge of the MWR antenna beam footprint geolocation is crucial to mission success. In particular, this thesis addresses an on-orbit validation of the MWR antenna beam pointing, using calculated MWR instantaneous field of view (IFOV) centers, provided in the CONAE L-1B science data product. This procedure compares L-1B MWR IFOV centers at land/water crossings against high-resolution coastline maps. MWR IFOV locations versus time are computed from knowledge of the satellite\u27s instantaneous location relative to an earth-centric coordinate system (provided by on-board GPS receivers), and a priori measurements of antenna gain patterns and mounting geometry. Previous conical scanning microwave radiometer missions (e.g., SSM/I) have utilized observation of rapid change in brightness temperatures (T_B) to estimate the location of land/water boundaries, and subsequently to determine the antenna beam-pointing accuracy. In this thesis, results of an algorithm to quantify the geolocation error of MWR beam center are presented, based upon two-dimensional convolution between each beam\u27s gain pattern and land-water transition. The analysis procedures have been applied to on-orbit datasets that represent land-water boundaries bearing specific desirable criteria, which are also detailed herein. The goal of this research is to gain a better understanding of satellite radiometer beam-pointing error and thereby to improve the geolocation accuracy for MWR science data products

Polarimetric Microwave Radiometer Calibration.

A polarimetric radiometer is a radiometer with the capability to measure the correlation information between vertically and horizontally polarized electric fields. To better understand and calibrate this type of radiometer, several research efforts have been undertaken. 1) All microwave radiometer measurements of brightness temperature (TB) include an additive noise component. The variance and correlation statistics of the additive noise component of fully polarimetric radiometer measurements are derived from theoretical considerations and the resulting relationships are verified experimentally. It is found that the noise can be correlated among polarimetric channels and that the correlation statistics can vary as a function of the polarization state of the scene under observation. 2) A polarimetric radiometer calibration algorithm has been developed which makes use of the Correlated Noise Calibration Standard (CNCS) to aid in the characterization of microwave polarimetric radiometers and to characterize the non-ideal characteristics of the CNCS itself simultaneously. CNCS has been developed by the Space Physics Research Laboratory of the University of Michigan (SPRL). The calibration algorithm has been verified using the DetMit L-band radiometer. The precision of the calibration is estimated by Monte Carlo simulations. A CNCS forward model has been developed to describe the non-ideal characteristics of the CNCS. Impedance-mismatches between the CNCS and radiometer under test are also considered in the calibration. 3) The calibration technique is demonstrated by applying it to the Engineering Model (EM) of the NASA Aquarius radiometer. CNCS is used to calibrate the Aquarius radiometer – specifically to retrieve its channel phase imbalance and the thermal emission characteristics of transmission line between its antenna and receiver. The impact of errors in calibration of the radiometer channel phase imbalance on Sea Surface Salinity (SSS) retrievals by Aquarius is also analyzed. 4) The CNCS has also been used to calibrate the Breadboard Model (BM) of the L-band NASA Juno radiometer. In order to cover the broad TB dynamic range of the Juno radiometer, a special linearization process has been developed for the CNCS. The method combines multiple Arbitrary Waveform Generator gaussian noise signals with different values of variance to construct the necessary range of TB levelsPh.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61741/1/jzhpeng_1.pd