Showing papers on "Radiometer published in 2010"

Diviner Lunar Radiometer Observations of Cold Traps in the Moon’s South Polar Region

Abstract: Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.

Light-driven nanoscale plasmonic motors

Abstract: When Sir William Crookes developed a four-vaned radiometer, also known as the light-mill, in 1873, it was believed that this device confirmed the existence of linear momentum carried by photons, as predicted by Maxwell's equations. Although Reynolds later proved that the torque on the radiometer was caused by thermal transpiration, researchers continued to search for ways to take advantage of the momentum of photons and to use it for generating rotational forces. The ability to provide rotational force at the nanoscale could open up a range of applications in physics, biology and chemistry, including DNA unfolding and sequencing and nanoelectromechanical systems. Here, we demonstrate a nanoscale plasmonic structure that can, when illuminated with linearly polarized light, generate a rotational force that is capable of rotating a silica microdisk that is 4,000 times larger in volume. Furthermore, we can control the rotation velocity and direction by varying the wavelength of the incident light to excite different plasmonic modes.

The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment

Abstract: The Diviner Lunar Radiometer Experiment on NASA’s Lunar Reconnaissance Orbiter will be the first instrument to systematically map the global thermal state of the Moon and its diurnal and seasonal variability. Diviner will measure reflected solar and emitted infrared radiation in nine spectral channels with wavelengths ranging from 0.3 to 400 microns. The resulting measurements will enable characterization of the lunar thermal environment, mapping surface properties such as thermal inertia, rock abundance and silicate mineralogy, and determination of the locations and temperatures of volatile cold traps in the lunar polar regions.

Design and Characterization of $W$ -Band SiGe RFICs for Passive Millimeter-Wave Imaging

Abstract: This paper describes the design and measurement of a wideband (W-band) passive radiometer chip developed in a standard 0.12-?m SiGe BiCMOS technology (IBM8HP, ft /fmax = 200/265 GHz). Design equations, simulations, and measurements are presented for a 94-GHz square-law detector and wideband low noise amplifier, and an 80-110-GHz single-pole double-throw switch. A total-power radiometer is presented, which can achieve a temperature resolution of ? 0.69 K (30-ms integration time) with periodic calibration or chopping above 10 kHz. A switched Dicke radiometer chip is also presented, which addresses the 1/f noise of the total-power radiometer, and can achieve a temperature resolution of 0.83 K with a 30-ms integration time. This performance is comparable to current III-V imaging modules, and demonstrates, to our knowledge, the first implementation of a SiGe or CMOS W -band radiometer on a single chip.

Comparisons of Daily Sea Surface Temperature Analyses for 2007–08

Abstract: Six different SST analyses are compared with each other and with buoy data for the period 2007–08. All analyses used different combinations of satellite data [for example, infrared Advanced Very High Resolution Radiometer (AVHRR) and microwave Advanced Microwave Scanning Radiometer (AMSR) instruments] with different algorithms, spatial resolution, etc. The analyses considered are the National Climatic Data Center (NCDC) AVHRR-only and AMSR+AVHRR, the Navy Coupled Ocean Data Assimilation (NCODA), the Remote Sensing Systems (RSS), the Real-Time Global High-Resolution (RTG-HR), and the Operational SST and Sea Ice Analysis (OSTIA); the spatial grid sizes were , respectively. In addition, all analyses except RSS used in situ data. Most analysis procedures and weighting functions differed. Thus, differences among analyses could be large in high-gradient and data-sparse regions. An example off the coast of South Carolina showed winter SST differences that exceeded 5°C. To help quantify SST analysis diff...

Accuracy of Satellite Sea Surface Temperatures at 7 and 11 GHz

Abstract: Satellite microwave radiometers capable of accurately retrieving sea surface temperature (SST) have provided great advances in oceanographic research. A number of future satellite missions are planned to carry microwave radiometers of various designs and orbits. While it is well known that the 11 GHz SST retrievals are less accurate than the 7 GHz retrievals, particularly in colder waters, it has not been demonstrated using existing microwave data. The Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) provides the means to examine the accuracies of SST retrievals using these channels in a systematic manner. In this paper, the accuracies of SSTs at 7 and 11 GHz are determined using two approaches: modeled and empirical. The modeled accuracies are calculated using an emissivity model and climatology SSTs, while empirical accuracies are estimated through validation of AMSR-E 7 and 11 GHz SST retrievals using over six years of data. It was found that the 7 GHz SST retrievals have less errors due to radiometer noise and geophysical errors than the 11 GHz retrievals at all latitudes. Additionally, while averaging the 11 GHz retrievals will diminish error due to uncorrelated radiometer noise, the geophysical error is still higher than for the 7 GHz retrievals, particularly at the higher latitudes.

A Novel Near-Land Radiometer Wet Path-Delay Retrieval Algorithm: Application to the Jason-2/OSTM Advanced Microwave Radiometer

Abstract: An algorithm is developed to retrieve wet tropospheric path delay (PD) near land from a satellite microwave radiometer to improve coastal altimetry studies Microwave radiometers are included on ocean altimetry missions to retrieve the wet PD, but their performance has been optimized for retrievals in the open ocean Near land, the radiometer footprint contains a mixture of radiometrically warm land and radiometrically cold ocean Currently, the radiometer retrievals in the coastal region are flagged as invalid since large errors result when the open-ocean retrieval algorithm is applied to mixed land/ocean scenes The PD retrieval algorithm developed in this paper is applicable to both open-ocean and mixed land-ocean scenes, thus enabling retrievals in the coastal zone The performance of the algorithm is demonstrated with detailed simulations and application to measurements from the Advanced Microwave Radiometer on the Jason-2/Ocean Surface Topography Mission The algorithm error is estimated to be less than 08 cm up to 15 km from land, less than 10 cm within 10 km from land, less than 12 cm within 5 km from land, and less than 15 cm up to the coastline

Satellite Microwave Remote Sensing of Daily Land Surface Air Temperature Minima and Maxima From AMSR-E

Abstract: We present an approach to retrieve daily minimum and maximum 2-m height air temperatures from 18.7, and 23.8 GHz H and V polarized brightness temperature from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) during the snow free season. The approach accounts, with minimal ancillary data, for vertically integrated atmospheric water vapor, and variable surface emissivity due to open water and vegetation. Retrieved temperatures were evaluated using Northern Hemisphere weather stations and independent satellite-based air temperatures from the Atmosphere Infrared Sounder and Advanced Microwave Sounding Unit (AIRS/AMSU; hereafter AIRS) sensors on Aqua. The retrieved temperatures are within 1.0 - 3.5 K of surface weather station measurements for vegetated locations, but uncertainty can exceed 4 K for desert and sparsely vegetated regions, mainly due to site to site biases. The AIRS and AMSR-E temperature retrievals generally agree more closely with one another than with weather stations and are generally within 1.0-2.8 K over vegetated regions, but with less agreement ( > 4 K ) over desert and mountainous regions. Additional useful information produced by our approach includes open water fraction, vegetation optical depth and atmospheric water vapor. The results of this study provide inputs for land surface models and a new approach for monitoring of land surface air temperatures with well quantified accuracy and precision.

ELBARA II, an L-Band Radiometer System for Soil Moisture Research

Abstract: L-band (1–2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is important for validating the satellite data and for the further improvement of the radiative transfer models used in the soil-moisture retrieval algorithms. To address these needs, three identical L-band radiometer systems were ordered by ESA. They rely on the proven architecture of the ETH L-Band radiometer for soil moisture research (ELBARA) with major improvements in the microwave electronics, the internal calibration sources, the data acquisition, the user interface, and the mechanics. The purpose of this paper is to describe the design of the instruments and the main characteristics that are relevant for the user.

L-Band RFI as Experienced During Airborne Campaigns in Preparation for SMOS

Abstract: In support of the European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission, a number of soil moisture and sea salinity campaigns, including airborne L-band radiometer measurements, have been carried out. The radiometer used in this context is fully polarimetric and has built-in radio-frequency-interference (RFI)-detection capabilities. Thus, the instrument, in addition to supplying L-band data to the geophysicists, also gave valuable information about the RFI environment. Campaigns were carried out in Australia and in a variety of European locations, resulting in the largest and most comprehensive data set available for assessing RFI at L-band. This paper introduces the radiometer system and how it detects RFI using the kurtosis method, reports on the percentage of data that are typically flagged as being corrupted by RFI, and gives a hint about geographical distribution. Also, examples of polarimetric signatures are given, and the possibility of detecting RFI using such data is discussed.

SLSTR: a high accuracy dual scan temperature radiometer for sea and land surface monitoring from space

Abstract: SLSTR is a high accuracy infrared radiometer which will be embarked in the Earth low-orbit Sentinel 3 operational GMES mission. SLSTR is an improved version of the previous AATSR and ATSR-1/2 instruments which have flown respectively on Envisat and ERS-1/2 ESA missions. SLSTR will provide data continuity with respect to these previous missions but with a substantial improvement due to its higher swaths (750 km in dual view and 1400 km in single view) which should permit global coverage of SST and LST measurements (at 1 km of spatial resolution in IR channels) with daily revisit time, useful for climatological and meteorological applications. Two more SWIR channels and a higher spatial resolution in the VIS/SWIR channels (0.5 km) are also implemented for a better clouds/aerosols screening. Two further additional channels for global scale fire monitoring are present at the same time as the other nominal channels.

Estimate of Phase Transition Water Content in Freeze–Thaw Process Using Microwave Radiometer

Abstract: Ground surface freeze-thaw cycles caused by changes in solar radiation have a great impact on soil-air water heat exchanges due to the phase transition of pore water. This influence should not be ignored in the land surface process and global environment change studies because of its large extent and the rapid changes in daily and seasonal frozen ground. The key index for evaluating the influence intensity is the content of water-ice phase transition in soil pores at the ground surface. In this paper, a data set was generated by observing field experiments and physical model simulations based on the configuration of the Advanced Microwave Scanning Radiometer-EOS (AMSR-E). The results showed that microwave radiation from freezing/thawing soil has an obvious correlation to the phase transition process of soil water. A large change in soil surface emissivity was shown after the freezing of soil. The magnitude of the difference in emissivity change is strongly related to the amount of water-ice phase transition. It can be shown that the higher the phase transition water content (PTWC), the greater the emissivity difference, and the higher the frequency, the smaller the emissivity difference. Based on an analysis of a large amount of random simulation data, an interesting characteristic was found, in that the emissivity difference in vertical polarization at each frequency is nearly proportional to the phase transition water content. Thus, a ratio index called Quasi-emissivity (Qe) was developed to eliminate temperature effects during retrieval. Using these clear rules, a physical statistical algorithm was put forth to estimate the phase transition water content. Finally, the inferred results by ground-based radiometer observation were compared with the ground truth. A satisfying agreement was achieved with a root mean square error of 0.0265 (v/v). This indicated that the microwave radiometer has a great potential in the measurement of PTWC.

Descent from the polar mesosphere and anomalously high stratopause observed in 8 years of water vapor and temperature satellite observations by the Odin Sub‐Millimeter Radiometer

Abstract: Using newly analyzed mesospheric water vapor and temperature observations from the Sub-Millimeter Radiometer instrument aboard the Odin research satellite over the period 2001-2009, we present evidence for an anomalously strong descent of dry mesospheric air from the lower mesosphere into the upper stratosphere in the winters of 2004, 2006, and 2009. In the three cases, the descent follows the recovery of the upper stratospheric polar vortex from a major midwinter stratospheric sudden warming. It is also accompanied by the rapid formation of an anomalously warm polar mesospheric layer, i.e., an elevated polar stratopause, near 75 km, and its slower descent to prewarming level (near 1 hPa) over 1.5-2 months. These three winters stand out in the current record of Odin/Sub-Millimeter Radiometer observations started in July 2001.

A far-infrared radiative closure study in the Arctic: Application to water vapor

Abstract: [1] Far-infrared (λ > 15.0 μm) (far-IR) radiative processes provide a large fraction of Earth's outgoing longwave radiation and influence upper tropospheric vertical motion. Water vapor, because of its abundance and strong absorption properties over an extended spectral range, is the primary source of these radiative processes. Historically, the lack of spectrally resolved radiometric instruments and the opacity of the lower atmosphere have precluded extensive studies of far-IR water vapor absorption properties. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program has organized a series of field experiments, the Radiative Heating in Underexplored Bands Campaigns (RHUBC), to address this deficiency. The first phase of RHUBC took place in 2007 at the ARM North Slope of Alaska Climate Research Facility. Measurements taken before and during this campaign have provided the basis for a clear-sky radiative closure study aimed at reducing key uncertainties associated with far-IR radiative transfer models. Extended-range Atmospheric Emitted Radiance Interferometer infrared radiance observations taken in clear sky conditions were compared against calculations from the Line-By-Line Radiative Transfer Model. The water vapor column amounts used in these calculations were retrieved from 183 GHz radiometer measurements. The uncertainty in these integrated water vapor retrievals is approximately 2%, a notable improvement over past studies. This far-IR radiative closure study resulted in an improvement to the Mlawer-Tobin Clough-Kneiyzs-Davies (MT_CKD) water vapor foreign continuum model and updates to numerous, far-IR water vapor line parameters from their values in the circa 2006 version of the HITRAN molecular line parameter database.

Using CALIPSO to explore the sensitivity to cirrus height in the infrared observations from NPOESS/VIIRS and GOES‐R/ABI

Abstract: [1] This paper demonstrates how the availability of specific infrared channels impacts the ability of two future meteorological satellite imagers to estimate cloud-top pressure. Both of the imagers are planned for launch by the United States, one for a geostationary platform and the other for a polar-orbiting platform. The geostationary imager, the Advanced Baseline Imager (ABI), will be flown first on the GOES-R platform. In addition to the split window channels at 11 and 12 μm, it has one spectral channel located at 13.3 μm where there is relatively strong absorption of H2O and CO2. The polar-orbiting imager, called the Visible/Infrared Imager Radiometer Suite (VIIRS) and flown on the National Polar-Orbiting Environmental satellite Suite (NPOESS), has spectral channels in window regions only. The lack of an absorbing channel on VIIRS is shown to have negative consequences for the inference of cloud-top pressure. This paper investigates the impact on the ability of a satellite imager such as VIIRS to confidently estimate cloud-top pressure due to the absence of infrared absorption channels. The solution space is defined as the depth of the atmospheric layer in which a cloud can be placed where the calculated top-of-atmosphere radiances match the measurements used in the cloud-top pressure retrieval. For optically thin cirrus, the channels used by the operational VIIRS algorithm provide a solution space of over 200 hPa. However, the inclusion of the single CO2 channel at 13.3 μm on the ABI narrows the solution space to under 30 hPa. Our imager-based analysis is performed using Moderate Resolution Imaging Spectroradiometer (MODIS) data, which provides the relevant channel information with sufficient spatial resolution and radiometric accuracy. Additional results are provided using data from the current GOES and POES imagers. Active lidar data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation/Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO/CALIOP) observations are used to provide cloud boundaries for verification.

Climatology of aerosol optical depth in north-central Oklahoma: 1992-2008

Abstract: [1] Aerosol optical depth (AOD) has been measured at the Atmospheric Radiation Measurement Program central facility near Lamont, Oklahoma, since the fall of 1992. Most of the data presented are from the multifilter rotating shadowband radiometer, a narrow‐band, interference‐filter Sun radiometer with five aerosol bands in the visible and near infrared; however, AOD measurements have been made simultaneously and routinely at the site by as many as three different types of instruments, including two pointing Sun radiometers. Scatterplots indicate high correlations and small biases consistent with earlier comparisons. The early part of this 16 year record had a disturbed stratosphere with residual Mt. Pinatubo aerosols, followed by the cleanest stratosphere in decades. As such, the last 13 years of the record reflect changes that have occurred predominantly in the troposphere. The field calibration technique is briefly described and compared to Langley calibrations from Mauna Loa Observatory. A modified cloud‐ screening technique is introduced that increases the number of daily averaged AODs retrieved annually to about 250 days compared with 175 days when a more conservative method was employed in earlier studies. AODs are calculated when the air mass is less than six; that is, when the Sun’s elevation is greater than 9.25°. The more inclusive cloud screen and the use of most of the daylight hours yield a data set that can be used to more faithfully represent the true aerosol climate for this site. The diurnal aerosol cycle is examined month‐by‐month to assess the effects of an aerosol climatology on the basis of infrequent sampling such as that from satellites.

An application of the SFIM technique to enhance the spatial resolution of spaceborne microwave radiometers

Abstract: Microwave radiometers operating from space are one of the most promising tools for soil, snow and vegetation monitoring, due to the sensitivity of the measured emission to surface features and to the extended and recursive Earth observation. However, these potentials are partially hampered by the coarse spatial resolution, which is of the order of tens of kilometres, especially at the lower frequencies. This paper describes the results obtained by using a simple algorithm for enhancing the spatial resolution of the spaceborne microwave radiometer at C-band. The algorithm is based on the smoothing filter-based intensity modulation technique (SFIM), applied to the Advanced Microwave Remote Scanning Radiometer-Earth Observing System (AMSR-E) data collected from some reference targets, including the Amazon river basin, Lake Victoria in Africa and the Antarctic plateau.

Planck-LFI: Design and Performance of the 4 Kelvin Reference Load Unit

Abstract: The LFI radiometers use a pseudo-correlation design where the signal from the sky is continuously compared with a stable reference signal, provided by a cryogenic reference load system. The reference unit is composed by small pyramidal horns, one for each radiometer, 22 in total, facing small absorbing targets, made of a commercial resin ECCOSORB CR (TM), cooled to approximately 4.5 K. Horns and targets are separated by a small gap to allow thermal decoupling. Target and horn design is optimized for each of the LFI bands, centered at 70, 44 and 30 GHz. Pyramidal horns are either machined inside the radiometer 20K module or connected via external electro-formed bended waveguides. The requirement of high stability of the reference signal imposed a careful design for the radiometric and thermal properties of the loads. Materials used for the manufacturing have been characterized for thermal, RF and mechanical properties. We describe in this paper the design and the performance of the reference system.

Simulation of Spaceborne Microwave Radiometer Measurements of Snow Cover Using In Situ Data and Brightness Temperature Modeling

Abstract: The Helsinki University of Technology (HUT) snow emission model is used to calculate the time series of brightness temperature of snow-covered sparsely forested area for the winter 2006-2007. Brightness temperature simulations that apply in situ observed physical parameters as input are compared with the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) observations. Three models for the extinction coefficient of snow and the statistical and physical atmospheric models are compared. Simulation results are presented with full in situ data set and only air temperature and snow depth (SD) as input data. The obtained results indicate that the extinction coefficient model of Hallikainen originally used with the HUT snow emission model is the best suited for the Finnish snow data set used in this paper and also on frequencies which are outside the original range of the extinction coefficient model. The simulation results obtained using only air temperature and SD input data show that the HUT snow model is quite reliable even with a minimal in situ data set. A time series of optimized grain sizes was calculated by minimizing the simulation error. The optimized grain size tended to saturate with large values, and therefore, a new model to calculate an effective grain size was developed. The simulation with the effective grain size as input has lower rms error and higher correlation with AMSR-E data than the simulation with the measured grain size.

Ultraviolet and vacuum-ultraviolet detector-based radiometry at the Metrology Light Source

Abstract: The Metrology Light Source (MLS) is a low-energy electron storage ring owned by the Physikalisch-Technische Bundesanstalt. It is optimized for basic radiometry and radiometric applications in the wavelength range from the terahertz to the extreme-ultraviolet spectral regime. As one of the basic tasks, detector-based radiometry is performed with a cryogenic electrical substitution radiometer as a primary detector standard. For the spectral range between 40 and 400 nm, the detector calibration facility was moved from its former site at the BESSY II storage ring with the beginning of user operation at the MLS in early 2008. In combination with a dedicated normal-incidence monochromator beamline, the spectral responsivities of photodetectors can be determined with relative uncertainties ranging from 1.1% down to 0.2% in the ultraviolet and vacuum-ultraviolet wavelength range. The beamline has several options to minimize high-order effects and comes with reliable intensity monitoring systems. Extensive characterization of the beamline properties has led to a detailed uncertainty budget.

Design and first results of an UAV-borne L-band radiometer for multiple monitoring purposes.

Abstract: UAV (unmanned Aerial Vehicle) platforms represent a challenging opportunity for the deployment of a number of remote sensors. These vehicles are a cost-effective option in front of manned aerial vehicles (planes and helicopters), are easy to deploy due to the short runways needed, and they allow users to meet the critical requirements of the spatial and temporal resolutions imposed by the instruments. L-band radiometers are an interesting option for obtaining soil moisture maps over local areas with relatively high spatial resolution for precision agriculture, coastal monitoring, estimation of the risk of fires, flood prevention, etc. This paper presents the design of a light-weight, airborne L-band radiometer for deployment in a small UAV, including the hardware and specific software developed for calibration, geo-referencing, and soil moisture retrieval. First results and soil moisture retrievals from different field experiments are presented.

Evaluation of AATSR and TMI Satellite SST Data

Abstract: The purpose of this paper is to investigate two satellite instruments for SST: the infrared (IR) Advanced Along Track Scanning Radiometer (AATSR) and the microwave (MW) Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). Because of its dual view, AATSR has a potential for lower biases than other IR products such as the Advanced Very High Resolution Radiometer (AVHRR), while the tropical TMI record was available for a longer period of time than the global MW instrument, the Advanced Microwave Scanning Radiometer (AMSR). The results show that the AATSR IR retrievals are good quality with biases lower than or as low as other satellite retrievals between 50°S and 50°N. Furthermore, the dual-view algorithm reduces the influence of aerosol contamination. However, the AATSR coverage is roughly half that of AVHRR. North of 50°N there appear to be biases and high variability in summer daytime retrievals, with smaller but consistent biases observed below 50°S. TMI data can significantly impr...

Method and apparatus for aligning an ablation catheter and a temperature probe for an ablation procedure

Abstract: Apparatus for aligning an ablation catheter and a temperature probe relatively for an ablation procedure includes an ablation catheter with a first antenna for ablating tissue at an ablation site in a patient's body and a temperature probe for placement in a body passage having a wall portion adjacent to the ablation site so that a second antenna in the probe is positioned opposite the first antenna. A microwave source provides a pulse modulated microwave signal to one of the antennas and a radiometer is in circuit with the other antenna. A synchronizing device in circuit with the microwave source and the radiometer enables the radiometer to synchronously detect the microwave signal so that the radiometer provides an alignment signal whose strength reflects the degree of alignment of the first and second antennas which signal may be used to control an alignment display. An alignment method using the apparatus is also disclosed.

An Improved C-Band Ocean Surface Emissivity Model at Hurricane-Force Wind Speeds Over a Wide Range of Earth Incidence Angles

Abstract: An improved microwave radiometric ocean surface emissivity model has been developed to support forward radiative transfer modeling of brightness temperature and geophysical retrieval algorithms for the next-generation airborne Hurricane Imaging Radiometer instrument. This physically based C-band emissivity model extends current model capabilities to hurricane-force wind speeds over a wide range of incidence angles. It was primarily developed using brightness temperature observations during hurricanes with coincident high-quality surface-truth wind speeds, which were obtained using the airborne Stepped-Frequency Microwave Radiometer. Also, other ocean emissivity models available through the published literature and the spaceborne WindSat radiometer measurements were used.