Fernando A. Pellerano

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.

The Thermal Infrared Sensor (TIRS) on Landsat 8: Design Overview and Pre-Launch Characterization

The Thermal Infrared Sensor (TIRS) on Landsat 8 is the latest thermal sensor in that series of missions. Unlike the previous single-channel sensors, TIRS uses two channels to cover the 10–12.5 micron band. It is also a pushbroom imager; a departure from the previous whiskbroom approach. Nevertheless, the instrument requirements are defined such that data continuity is maintained. This paper describes the design of the TIRS instrument, the results of pre-launch calibration measurements and shows an example of initial on-orbit science performance compared to Landsat 7.

Mitigation of Terrestrial Radar Interference in L-Band Spaceborne Microwave Radiometers

Terrestrial radars operating in the 1215-1400 MHz radio-location and navigation spectrum allocation are important for air traffic safety, homeland security, and national defense. For low-frequency observations of soil moisture and ocean salinity, Earth-observing microwave radiometers are allocated EarthExploration Satellite Service (EESS) spectrum for operating at 1400-1427 MHz. The proximity of powerful long-range radars to the passive allocation makes observing a challenge. Three aspects of mitigation to RFI are discussed in this paper: survivability, operability, and excisability (SOE). Modeling and simulations of NASAs Hydros and Aquarius radiometers were performed to examine the impacts of radar interference. The results are applied to the three aspects of mitigation SOE and the affects on the radiometer requirements are discussed. The physics of microwave thermal emission dictate that low frequencies be used for radiometers to measure ocean-surface salinity and soil moisture (through any reasonable amount of vegetation). The Earth Exploration Satellite Service (EESS) enjoys an exclusive passive allocation at 1400-1427 MHz, a band in which transmission is prohibited [I]. Two L-band microwave radiometers will be launched into orbit before the decades end. (It was three until NASA canceled its Hydros mission [2] to measure global soil moisture and freeze-thaw state see http:/ihydros.~sfc.nasa.gov). NASAs Aquarius radiometer will measure ocean surface salinity on a global scale [3] and ESAs SMOS mission will measure soil moisture [4]. If radiometer receivers where perfectly selective to their allocated band and neighboring transmitters had perfect control of outof-band (OOB) emissions, radio-frequency interference (RFI) would not be an issue. Experience shows, however, this is not the case [5]-[8]. Since no L-band radiometers have flown in space since Skylab, airborne and ground-based experience augmented by analysis must be used to predict the potential impact of the spectrum environment. By experience, the most problematic interference is due to terrestrial radars TRs and a previous analysis for SMOS also predicts this to be the case [91. In this paper, the impacts of interference due to TRs operating below 1400 M H ~ on the engineering requirements of Aquarius and Hydros are analyzed. The RFI analyses herein are from a study of TRs commissioned by the NASA Earth Science Spectrum Management Office for the Aquarius and Hydros missions [lo]. Given the impacts, three aspects to mitigation are proposed: survivability, operability, and excisability; or SOE. Survivability deals with avoiding damage from RFI. This means proper filtering and limiting. A radiometer achieves operability when it can measure, without error, the antenna or brightness temperature in the presence of interference. Selective receivers operating in quite spectrum are required for operability. When filtering and frequency selection is not enough to avoid interference, then the RFI might be excisable. A number of techniques have been proposed and demonstrated recently [Ill-[14]. These fall into three basic categories: temporal, spectral, and statistical some techniques are a combination of two or more. We draw a distinction between operability and excisability when signal analysis beyond conventional radiometric techniques is required. The Aquarius and Hydros approaches to SOE are

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 ~120 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand) [1]. This requires an L-band low-noise radiometer with the long-term calibration stability of les0.15 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 0.1degCrms over 7 days.

Aquarius Mission Technical Overview

Aquarius is an L-band microwave instrument being developed to map the surface salinity field of the oceans from space. It is part of the Aquarius/SAC-D mission, a partnership between the USA (NASA) and Argentina (CONAE) with launch scheduled for early in 2009. 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.

Development of a high stability L-band radiometer for ocean salinity measurements

An NEDT analysis of a Dicke radiometer with noise diode injection is presented. The analysis is formulated for a calibration that would form separate running averages of receiver noise temperature and of gain in order to minimize the NEDT and maximize the antenna observation duty cycle relative to the reference and noise diode duty cycles. Results are applied to the Aquarius ocean salinity radiometer problem to show that near ideal total-power radiometer performance is possible.

The measurement of salinity from space: sensor concept

Salinity in the open ocean is important for understanding ocean dynamics and for modeling energy exchange with the atmosphere. The potential exists for obtaining global coverage of sea surface salinity using a microwave sensor in space operating at L-band (1.4 GHz). Work is currently underway at NASAs Goddard Space Flight Center and the Jet Propulsion Laboratory to define a sensor to make this measurement from space. The goal is to achieve spatial resolution on the order of 100 km with a revisit time of 14 days or less and a calibration accuracy equivalent to 0.2 psu. It is planned to combine the radiometer with a radar to help correct for surface roughness. It is believed that such a sensor system can be developed within the confines of a future Earth Sensor System Pathfinder (ESSP) mission.

The Aquarius/SAC-D mission and status of the Aquarius instrument

The Aquarius/SAC-D mission is a partnership between the USA (NASA) and Argentina (CONAE). The observatory consists of Aquarius, an L-band radiometer/radar combination being developed under NASApsilas Earth System Science Pathfinder (ESSP) program to map the surface salinity field of the oceans from space, together with the SAC-D bus and several instruments provided by CONAE and its partners. The Aquarius instrument is currently in I&T at NASA/JPL. The mission is scheduled for launch in May, 2010.

Aquarius: A Mission to Monitor Sea Surface Salinity from Space

Aquarius is a combination passive/active L-band microwave instrument being developed to map the surface salinity field of the oceans from space. It is part of the Aquarius/SAC-D mission, a partnership between the USA (NASA) and Argentina (CONAE) with launch scheduled for early in 2009. 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

Development of a high-stability microstrip-based L-band radiometer for ocean salinity measurements

The development of a microstrip-based L-band Dicke radiometer with the long-term stability required for future ocean salinity measurements to an accuracy of 0.1 psu is presented. This measurement requires the L-band radiometers to have calibration stabilities of les 0.05 K over 2 days. This research has focused on determining the optimum radiometer requirements and configuration to achieve this objective. System configuration and component performance have been evaluated with radiometer test beds at both JPL and GSFC. The GSFC test bed uses a cryogenic chamber that allows long-term characterization at radiometric temperatures in the range of 70 - 120 K. The research has addressed several areas including component characterization as a function of temperature and DC bias, system linearity, optimum noise diode injection calibration, and precision temperature control of components. A breadboard radiometer, utilizing microstrip-based technologies, has been built to demonstrate this long-term stability