Showing papers on "Radiometer published in 2003"

AIRS/AMSU/HSB on the Aqua mission: design, science objectives, data products, and processing systems

Abstract: The Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), and the Humidity Sounder for Brazil (HSB) form an integrated cross-track scanning temperature and humidity sounding system on the Aqua satellite of the Earth Observing System (EOS). AIRS is an infrared spectrometer/radiometer that covers the 3.7-15.4-/spl mu/m spectral range with 2378 spectral channels. AMSU is a 15-channel microwave radiometer operating between 23 and 89 GHz. HSB is a four-channel microwave radiometer that makes measurements between 150 and 190 GHz. In addition to supporting the National Aeronautics and Space Administration's interest in process study and climate research, AIRS is the first hyperspectral infrared radiometer designed to support the operational requirements for medium-range weather forecasting of the National Ocean and Atmospheric Administration's National Centers for Environmental Prediction (NCEP) and other numerical weather forecasting centers. AIRS, together with the AMSU and HSB microwave radiometers, will achieve global retrieval accuracy of better than 1 K in the lower troposphere under clear and partly cloudy conditions. This paper presents an overview of the science objectives, AIRS/AMSU/HSB data products, retrieval algorithms, and the ground-data processing concepts. The EOS Aqua was launched on May 4, 2002 from Vandenberg AFB, CA, into a 705-km-high, sun-synchronous orbit. Based on the excellent radiometric and spectral performance demonstrated by AIRS during prelaunch testing, which has by now been verified during on-orbit testing, we expect the assimilation of AIRS data into the numerical weather forecast to result in significant forecast range and reliability improvements.

Soil moisture retrieval from AMSR-E

Abstract: The Advanced Microwave Scanning Radiometer (AMSR-E) on the Earth Observing System (EOS) Aqua satellite was launched on May 4, 2002. The AMSR-E instrument provides a potentially improved soil moisture sensing capability over previous spaceborne radiometers such as the Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager due to its combination of low frequency and higher spatial resolution (approximately 60 km at 6.9 GHz). The AMSR-E soil moisture retrieval approach and its implementation are described in this paper. A postlaunch validation program is in progress that will provide evaluations of the retrieved soil moisture and enable improved hydrologic applications of the data. Key aspects of the validation program include assessments of the effects on retrieved soil moisture of variability in vegetation water content, surface temperature, and spatial heterogeneity. Examples of AMSR-E brightness temperature observations over land are shown from the first few months of instrument operation, indicating general features of global vegetation and soil moisture variability. The AMSR-E sensor calibration and extent of radio frequency interference are currently being assessed, to be followed by quantitative assessments of the soil moisture retrievals.

The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), NASDA's contribution to the EOS for global energy and water cycle studies

Abstract: The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was developed and provided to the National Aeronautics and Space Administration's EOS Aqua satellite by the National Space Development Agency of Japan, as one of the indispensable instruments for Aqua's mission. AMSR-E is a modified version of AMSR that was launched December 2002 aboard the Advanced Earth Observing Satellite-II (ADEOS-II). It is a six-frequency dual-polarized total-power passive microwave radiometer that observes water-related geophysical parameters supporting global change science and monitoring efforts. The hardware improvements over existing spaceborne microwave radiometers for Earth imaging include the largest main reflector of its kind and addition of 6.925-GHz channels. These improvements provide finer spatial resolution and the capability to retrieve sea surface temperature and soil moisture information on a global basis. This paper provides an overview of the instrument characteristics, mission objectives, and data products.

Spaceborne soil moisture estimation at high resolution: a microwave-optical/IR synergistic approach

Abstract: An approach is evaluated for the estimation of soil moisture at high resolution using satellite microwave and optical/infrared (IR) data. This approach can be applied to data acquired by the Visible/Infrared Imager Radiometer Sensor Suite (VIIRS) and a Conical Scanning Microwave Imager/Sounder (CMIS), planned for launch in the 2009–2010 time frame under the National Polar-Orbiting Operational Environmental Satellite System (NPOESS). The approach for soil moisture estimation involves two steps. In the first step, a passive microwave remote sensing technique is employed to estimate soil moisture at low resolution (∼25 km). This involves use of a simplified radiative transfer model to invert dual-polarized microwave brightness temperature. In the second step, the microwave-derived low-resolution soil moisture is linked to the scene optical/IR parameters, such as Normalized Difference Vegetation Index (NDVI), surface albedo, and Land Surface Temperature (LST). The linking is based on the ‘Universal Triangle’ ...

The Odin satellite - I. Radiometer design and test

Abstract: The Sub-millimetre and Millimetre Radiometer (SMR) is the main instrument on the Swedish, Canadian, Finnish and French spacecraft Odin. It consists of a 1.1 metre diameter telescope with four tuneable heterodyne receivers covering the ranges 486-504 GHz and 541-581 GHz, and one fixed at 118.75 GHz together with backends that provide spectral resolution from 150 kHz to 1 MHz. This Letter describes the Odin radiometer, its operation and performance with the data processing and calibration described in Paper II.

A multichannel radiometric profiler of temperature, humidity, and cloud liquid

Abstract: [1] A microwave radiometer is described that provides continuous thermodynamic (temperature, water vapor, and moisture) soundings during clear and cloudy conditions. The radiometric profiler observes radiation intensity at 12 microwave frequencies, along with zenith infrared and surface meteorological measurements. Historical radiosonde and neural network or regression methods are used for profile retrieval. We compare radiometric, radiosonde, and forecast soundings and evaluate the accuracy of radiometric temperature and water vapor soundings on the basis of statistical comparison with radiosonde soundings. We find that radiometric soundings are equivalent in accuracy to radiosonde soundings when used in numerical weather forecasting. A case study is described that demonstrates improved fog forecasting on the basis of variational assimilation of radiometric soundings. The accuracy of radiometric cloud liquid soundings is evaluated by comparison with cloud liquid sensors carried by radiosondes. Accurate high-resolution three-dimensional water vapor and wind analysis is described on the basis of assimilation of simulated thermodynamic and wind soundings along with GPS slant delays. Examples of mobile thermodynamic and wind profilers are shown. Thermodynamic profiling, particularly when combined with wind profiling and slant GPS, provides continuous atmospheric soundings for improved weather and dispersion forecasting.

Satellite Estimates of Wind Speed and Latent Heat Flux over the Global Oceans

Abstract: Surface fluxes of momentum, freshwater, and energy across the air–sea interface determine oceanic circulation and its variability at all timescales. The goal of this paper is to estimate and examine some ocean surface flux variables using satellite measurements. The remotely sensed data come from the European Remote Sensing (ERS) satellite scatterometer on ERS-2, NASA scatterometer (NSCAT), and several Defense Meteorological Satellite Program (DMSP) radiometers [Special Sensor Microwave Imager (SSM/I)] on board the satellites F10–F14. The sea surface temperature comes from daily analysis calculated from Advanced Very High Resolution Radiometer (AVHRR) measurements. This study focuses on the 9-month period (October 1996–June 1997) of the NSCAT mission. To ensure high quality of the merged surface parameter fields, comparisons between different satellite estimates for the same variable have been performed, and bias corrections have been applied so that they are compatible with each other. The satel...

A consolidated technique for enhancing desert dust storms with MODIS

Abstract: [1] A new satellite-based multispectral passive radiometer technique for daytime enhancement of airborne dust over water and land has been developed. The algorithm, which combines color information from multiple visible channels with near and far infrared measurements, provides an improved ability to distinguish areas of dust from water/ice clouds and bright desert backgrounds in enhanced false-color imagery. While generally applicable to any sensor possessing the requisite spectral information, the method is demonstrated here using high spatial and spectral resolution digital data from the Moderate Imaging Spectroradiometer (MODIS) instruments carried aboard Earth Observing System (EOS) Terra and Aqua polar orbiter platforms.

Estimation of sensible heat flux using the Surface Energy Balance System (SEBS) and ATSR measurements

Abstract: This paper describes a modified version of the Surface Energy Balance System (SEBS) as regards the use of radiometric data from space and presents the results of a large area validation study on estimated sensible heat flux, extended over several months. The improvements were made possible by the characteristics of the Along Track Scanning Radiometer (ATSR-2) on board the European Remote Sensing satellite (ERS-2) and relate to: (a) the use of bi-angular radiometric data in two thermal infrared channels to estimate column atmospheric water vapor: (b) the use of bi-angular radiometric data in four spectral channels in the 550-1600 nm spectral regions to estimate aerosols optical depth: (c) determination of bottom of atmosphere (BOA) spectral reflectance using column water vapor, aerosols optical depth and a two-stream radiative transfer scheme to relate BOA spectral reflectance to top of atmosphere spectral radiance (d) direct and inverse modeling of radiative transfer in a vegetation canopy to relate BOA spectral reflectance to canopy properties, such as spectrally integrated hemispherical reflectance (albedo). A parameterization of the aerodynamic resistance for heat transfer (in term of kB(-1)) was applied for the first time at large spatial scales. For such large area analyses SEBS requires wind speed, potential temperature and humidity of air at an appropriate reference height. The latter was taken as being the height of the planetary boundary layer (PBL) and the data used were fields generated by an advanced numerical weather prediction model, i.e. regional atmospheric climate model (RACMO), integrated over the PBL. Validation of estimated sensible heat flux H obtained with the ATSR radiometric data was done using long-range, line-averaged measurements of H done with large aperture scintillometers (LAS) located at three sites in Spain and operated continuously between April and September 1999. The root mean square deviation of SEBS H estimates from LAS H measurements was 25.5 W m(-2). (C) 2003 Elsevier Science Ltd. All rights reserved.

Electron cyclotron emission radiometer upgrade on the DIII-D tokamak

Abstract: The electron cyclotron emission (ECE) heterodyne radiometer diagnostic on DIII-D has been upgraded with the addition of eight channels for a total of 40 The new, higher frequency channels allow measurements of electron temperature into the magnetic axis in discharges at maximum field, 215 T The complete set now extends over the full usable range of second harmonic emission frequencies at 20 T, covering radii from the outer edge inward to the location of third harmonic overlap on the high-field side Full coverage permits the measurement of heat pulses and magnetohydrodynamic fluctuations on both sides of the magnetic axis In addition, the symmetric measurements are used to fix the location of the magnetic axis in tokamak magnetic equilibrium reconstructions Also, the new, higher frequency channels have been used to determine central Te with good time resolution in low-field, high-density discharges using third harmonic ECE in the optically gray and optically thick regimes

Aerosol retrievals from AVHRR radiances: effects of particle nonsphericity and absorption and an updated long-term global climatology of aerosol properties

Abstract: The paper describes and discusses long-term global retrievals of aerosol properties from channel-1 and -2 Advanced Very High-Resolution Radiometer (AVHRR) radiances. We reconfirm the previously reached conclusion that the nonsphericity of dust-like and dry sea salt aerosols can lead to very large errors in the retrieved optical thickness if one mistakenly applies the scattering model for spherical particles. Comparisons of single-scattering albedo and A ngstrom exponent values retrieved from the AVHRR data and those measured in situ at Sable Island indicate that the currently adopted value 0.003 can be a reasonable choice for the imaginary part of the aerosol refractive index in the global satellite retrievals. Several unexpected features in the long-term satellite record indicate a serious problem with post-launch calibration of channel-2 radiances from the NOAA-11 spacecraft. We solve this problem by using a simple re-calibration procedure removing the observed artifacts and derive a global climatology of aerosol optical thickness and size over the oceans for the period extending from July 1983 to December 1999. The global monthly mean optical thickness and A ngstrom exponent of tropospheric aerosols show no significant trends over the entire period and oscillate around the average values 0.145 and 0.75, respectively. The Northern Hemisphere mean optical thickness systematically exceeds that averaged over the Southern Hemisphere. The AVHRR retrieval results during the period affected by the Mt. Pinatubo eruption are consistent with the retrievals of the stratospheric aerosol optical thickness based on Stratospheric Aerosol and Gas Experiment Data (SAGE). Time series of the aerosol optical thickness and A ngstrom exponent derived for four separate geographic regions exhibit varying degrees of seasonal variability controlled by local meteorological events and/or anthropogenic activities.

Accuracy of cloud liquid water path from ground-based microwave radiometry 2. Sensor accuracy and synergy

Abstract: [1] The influence of microwave radiometer accuracy on retrieved cloud liquid water path (LWP) was investigated. Sensor accuracy was assumed to be the sum of the relative (i.e., Gaussian noise) and the absolute accuracies of brightness temperatures. When statistical algorithms are developed the assumed noise should be as close as possible to the real measurements in order to avoid artifacts in the retrieved LWP distribution. Typical offset errors of 1 K in brightness temperatures can produce mean LWP errors of more than 30 g m−2 for a two-channel radiometer retrieval, although positively correlated brightness temperature offsets in both channels reduce this error to 16 g m−2. Large improvements in LWP retrieval accuracy of about 50% can be achieved by adding a 90-GHz channel to the two-channel retrieval. The inclusion of additional measurements, like cloud base height from a lidar ceilometer and cloud base temperature from an infrared radiometer, is invaluable in detecting cloud free scenes allowing an indirect evaluation of LWP accuracy in clear sky cases. This method was used to evaluate LWP retrieval algorithms based on different gas absorption models. Using two months of measurements, the Liebe 93 model provided the best results when the 90-GHz channel was incorporated into the standard two-channel retrievals.

Radiometric measurements of the sea-surface skin temperature: the competing roles of the diurnal thermocline and the cool skin

Abstract: It has long been recognized that satellite-borne infrared radiometers measure radiance that is more closely related to the temperature of the skin of the ocean than the sub-surface bulk temperature, but, historically, atmospheric correction algorithm derivation and validation exercises have been conducted using bulk temperatures measured at a depth of a metre or more. A recent validation of sea-surface temperature (SST) fields derived from the Advanced Very High Resolution Radiometer (AVHRR) with skin temperature measurements of the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) revealed a very low mean bias error, much smaller than was expected, given the thermal skin effect which acts to cool the surface with respect to sub-surface values by several tenths of a degree. This result does not imply the skin effect is unimportant-its effect is now well documented in many datasets-but that its effect is being partially compensated by diurnal heating effects. The evidence for this is presented an...

Thermal–infrared emissivities of natural surfaces: improvements on the experimental set-up and new measurements

Abstract: Ground measurements of thermal infrared emissivities of terrestrial surfaces are required to derive accurate temperatures from radiometric measurements, and also to apply and validate emissivity models using satellite sensor observations. This paper focuses on the demanding aspects that are involved in the field measurement of emissivity using the box method and a hand-held radiometer. Measuring emissivities in field conditions can be hampered by external factors such as wind and solar irradiance. This can increase the time spent on the field campaign but, most importantly, it can cause no-sense fluctuations between consecutive observations. Here we propose original developments for the experimental instrumentation to ensure consistency of measurements. Moreover, we present a dataset of emissivity values for different soils, rocks and vegetation samples measured in the 8–14, 8.2–9.2, 10.5–1 1.5 and 11.5–12.5 µm wavebands.

High-accuracy radiometry in the EUV range at the PTB soft x-ray beamline

Abstract: During the past decade, high-accuracy soft x-ray radiometry has increasingly gained in importance. In particular, its routine availability is a prerequisite for the development of extreme UV lithography (EUVL). The PTB has been providing EUV calibration services for many years at a dedicated radiometry beamline at the electron storage ring BESSY I and from the year 2000 at the new PTB synchrotron radiation laboratory at BESSY II. Reflectometry, especially the measurement of the reflectance of Mo/Si multilayer mirrors for EUVL, is a major activity at the beamline. As the performance of the third-generation storage ring BESSY II is better than that of BESSY I, the measurement uncertainties could be significantly reduced. Efforts were made to accurately determine the wavelength scale for the monochromator and to suppress diffusely scattered light. For the spectral reflectance of a mirror in the EUV spectral region, a relative uncertainty of u = 0.14% is achieved. A new reflectometer will enable PTB to characterize EUVL optics up to 550 mm in diameter and 50 kg in mass. Detector calibration is based on a primary detector standard, a cryogenic electrical substitution radiometer. Photodiodes with a nearly constant spectral responsitivity in the soft x-ray range are calibrated as transfer detector standards with a relative uncertainty of u = 0.26% by direct comparison to the radiometer.

First-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: On-Orbit Radiometer Characterization

Abstract: The WMAP satellite has completed 1 year of measurements of the cosmic microwave background (CMB) radiation using 20 differential high electron mobility transistor (HEMT) based radiometers. All the radiometers are functioning nominally, and characterizations of the on-orbit radiometer performance are presented, with an emphasis on properties that are required for the production of sky maps from the time-ordered data. A radiometer gain model, used to smooth and interpolate the CMB dipole gain measurements, is also presented. No degradation in the sensitivity of any of the radiometers has been observed during the first year of observations.

A new approach for retrieving precipitable water from ATSR2 split-window channel data over land area

Abstract: This paper presents a new algorithm to determine quantitatively column water vapour content ( W ) directly from ATSR2 (Along-Track Scanner Radiometer) Split-Window radiance measurements. First, the Split-Window Covariance-Variance Ratio (SWCVR) method is reviewed. The assumptions made to derive this method are highlighted and its applicability is discussed. Then, an operational use of this method is developed and applied to several ATSR2 datasets. The water vapour contents retrieved using ATSR2 data from SGP'97 (USA), Barrax (Spain) and Cabauw (The Netherlands) are in good agreement with those measured by the quasi-simultaneous radiosonde. The mean and the standard deviation of their difference are 0.04 g cm -2 and 0.22 g cm -2 , respectively. It is shown that water vapour content derived from ATSR2 data using the proposed algorithm is accurate enough in most cases for surface temperature determination with a split-window technique using ATSR2 data and for atmospheric corrections in visible and near-infrared channels of ATSR2.

In situ determination of the quantum yield of phytoplankton chlorophyll a fluorescence: A simple algorithm, observations, and a model

Abstract: Vertical profiles of the in situ quantum yield of fluorescence of chlorophyll a, ff, were derived with an algorithm from spectral underwater radiometer measurements. Select inherent optical properties were obtained from an initial radiance reflectance inversion that was optimized by comparing retrieved estimates of phytoplankton absorption with independent measurements. The comparison of chlorophyll concentrations produced by the algorithm to measured values allowed validation of the inversion. Fluorescence quantum yield values were calculated from the retrieved phytoplankton absorption and the upwelling radiance corrected for elastic and inelastic scattering. Raman scattered light was found to be a significant component of the upwelling light field at wavelengths of Chla fluorescence. Values of ff determined using the algorithm, and therefore derived solely from the radiometer measurements, were not significantly different from those estimated using independent measurements of absorption by phytoplankton (r 2 5 0.86). The profiles of ff were characterized by an initial increase with depth to a subsurface maximum followed by a subsequent decrease. The irradiances of the subsurface maxima and ff at high irradiances appeared to be well conserved. An irradiance-based model including photochemical and nonphotochemical quenching was developed to explain variations in the quantum yield.

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)

Abstract: The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) launched on NASA's Terra satellite in December 1999 provides anew tool for Earth observations. ASTER provides high-resolution, 15m(VNIR), 30m (SWIR) and 90m (TIR) coverage for limited areas with unique multispectal SWIR and TIR coverage and 15 m stereo coverage for DEM generation. These data have been used extensively for volcano and glacier monitoring. ASTER observations of over 1000 volcanoes around the world represent a significant increase in our ability to monitor volcanic activity and to map the products of eruptions. The SWIR channels have been used for mapping hot areas with temperatures up to 350 C and the multispectral TIR data have been used to map ash and SO2 plumes. ASTER data are being used in the Global Land Ice Measurements from Space (GLIMS) project to map and catalog the approximately 80,000 glaciers. The objective is to acquire multiple observations to detect changes in ice margins and surface feature velocities. ASTER data acquired over the Jornada Experimental range in New Mexico have been used to extract spectral emissivities in the 8 to 12 micrometer range. These TIR data were also used in models to estimate the surface energy fluxes. Similar analysis of data acquired over the El Reno Oklahoma test site has shown that our satellite estimates of the surface fluxes agree reasonably well with ground measurements.

Sea surface salinity from space: Science goals and measurement approach

Abstract: [1] Aquarius is a NASA/Earth System Science Pathfinder (ESSP) mission that proposes to make the first-ever global measurements of sea surface salinity. These measurements will enable improved understanding of oceanic thermohaline circulation and of the changes in oceanic circulation that are related to seasonal to interannual climate variability. Aquarius science goals also address tropical ocean-climate feedbacks and freshwater budget components of the coupled ocean-atmosphere system. These oceanographic science requirements for Aquarius dictate measurements of global sea surface salinity that are accurate to 0.2–0.3 psu, as averaged monthly and over 100–200 km areas. Key aspects of the Aquarius salinity mission design include the instrument with its high-stability L-band radiometers, the precise calibration of the measurements, and the salinity retrieval algorithm. The Aquarius mission will meet the science needs by providing complete global coverage of ocean surface salinity, with an 8 day cycle of observations using a three beam, L-band radiometer/scatterometer flying in a 6 am/6 pm polar orbit. This conceptual design has been verified using observations from aircraft flight instruments. The radiometer design for the instrument and the needed precise calibration is based on proven, temperature-stabilized radiometer designs with internal references, plus vicarious calibration approaches developed in the course of previous space missions.

The Advanced Very High Resolution Radiometer Pathfinder Atmosphere (PATMOS) Climate Dataset: A Resource for Climate Research

Abstract: As part of the joint National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) Pathfinder program, the NOAA National Environmental Satellite, Data, and Information Service (NESDIS) has created a research-quality global atmospheric dataset through the reprocessing of Advanced Very High Resolution Radiometer (AVHRR) observations since 1981. The AVHRR is an imaging radiometer that flies on NOAA polar-orbiting operational environmental satellites (POES) measuring radiation reflected and emitted by the earth in five spectral channels. Raw AVHRR observations were recalibrated using a vicarious calibration technique for the reflectance channels and an appropriate treatment of the nonlinearity of the infrared channels. The observations are analyzed in the Pathfinder Atmosphere (PATMOS) project to obtain statistics of channel radiances, cloud amount, top of the atmosphere radiation budget, and aerosol optical thickness over ocean. The radiances and radiation bu...

An assessment of microwave absorption models and retrievals of cloud liquid water using clear‐sky data

Abstract: [1] Passive microwave radiometers have a long history in the remote sensing of atmospheric liquid and water vapor. Retrievals of these quantities are sensitive to variations in pressure and temperature of the liquid and water vapor. Rather than use a statistical or climatological approach to account for the natural variability in atmospheric pressure and temperature, additional information on the atmospheric profile at the time of the radiometer measurements can be directly incorporated into the retrieval process. Such an approach has been referred to in the literature as a “physical-iterative” solution. This paper presents an assessment of the accuracy of the column liquid water path that can be expected using such an iterative technique as a result of uncertainties in the microwave emissions from oxygen and water vapor. It is shown that the retrieval accuracy is influenced by the accuracy of the instrument measurements and the quality of the atmospheric profiles of temperature and pressure, as one would expect. However, also critical is the uncertainty in the absorption coefficients used in the underlying microwave radiative transfer model. The uncertainty in the absorption coefficients is particularly problematic in that it may well bias the liquid water retrieval. The differences between three absorption models examined in this paper are equivalent to a bias of 15 to 30 g/m2, depending on the total column water vapor. An examination of typical liquid water paths from the Southern Great Plains region of the United States shows that errors of this magnitude have significant implications for shortwave radiation and retrievals of cloud effective particle size.

Effect of wavelength selection on characterization of fire size and temperature

Abstract: Over the past two decades, Dozier's 1981 retrieval method has been used with observations from various moderate-resolution (∼ 1 km) spaceborne sensors to estimate the instantaneous sub-pixel area and temperature of wildfires. The method requires simultaneous observations at two different wavelengths. Traditionally these wavelengths have resided in the middle- and long-wave infrared regions, for example the 4 and 11 @m channels of the NOAA Advanced Very High Resolution Radiometer (AVHRR). Development of recent and upcoming sensors, including the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible/Infrared Imager/Radiometer Suite (VIIRS), have spawned interest in using other wavelength combinations, particularly in the short-wave infrared, for sub-pixel active fire characterization. We demonstrate that for realistic wildfires, which are composed of both flaming and smouldering components, the location of these two wavelengths can cause large differences in the fire temperatures and areas t...

Soil moisture retrieval using the passive/active L- and S-band radar/radiometer

Abstract: In the present study, remote sensing of soil moisture is carried out using the Passive and Active L- and S-band airborne sensor (PALS) The data in this paper were taken from five days of overflights near Chickasha, OK during the 1999 Southern Great Plains (SGP99) experiment Presently, we analyze the collected data to understand the relationships between the observed signals (radiometer brightness temperature and radar backscatter) and surface parameters (surface soil moisture, temperature, vegetation water content, and roughness) In addition, a radiative transfer model and two radar backscatter models are used to simulate the PALS observations An integration of observations, regression retrievals, and forward modeling is used to derive the best estimates of soil moisture under varying surface conditions

SST availabilities of satellite infrared and microwave measurements

Abstract: To investigate the feasibility and methodology of new generation sea surface temperature (SST) maps that combine various satellite measurements, we have quantitatively evaluated SST availabilities of NOAA AVHRR (National Oceanic and Atmospheric Administration, Advanced Very High Resolution Radiometer), GMS S-VISSR (Geostationary Meteorological Satellite, Stretched-Visible Infrared Spin Scan Radiometer) and TRMM MI (Tropical Rainfall Measuring Mission, Microwave Imager: TMI), during the one-year period from October 1999 to September 2000. The advantage of satellite microwave SST measurements is the ability to penetrate the clouds that contaminate satellite infrared measurements. Daily SST availabilities were calculated in the overlapping coverage from 20°N to 38°N and 120°E to 160°E. The annual-mean SST availabilities of AVHRR, S-VISSR and TMI are 48%, 56% and 78%, respectively. There are large seasonal variations in the availabilities of infrared measurements. The latitude-time plots of one-degree zonal mean SST availabilities of S-VISSR and TMI in the region from 38°S to 38°N and 80°E to 160°W show significant zonal variations, which are influenced by the atmospheric circulation such as the Subtropical High and the Intertropical Convergence Zone. The SST availabilities of S-VISSR and TMI in the five selected regions have large regional variations, ranging from 35% to 74% and 62% to 88% for S-VISSR and TMI, respectively. The present statistical analyses of SST availabilities in the infrared and microwave measurements indicate that 1) a daily cloud-free high-spatial resolution may be achieved by merging various SST measurements since their deficiencies compensate each other, and 2) nevertheless, it is necessary to take account of the seasonal and regional variations of SST availabilities of different satellite sensors for the development of merging technology.

Multisensor analysis of integrated atmospheric water vapor over Canada and Alaska

Abstract: [1] Atmospheric water vapor is a key parameter for the analysis of climatic systems (greenhouse gas effect), in particular over high latitudes where water vapor displays an important seasonal variability. The sparse spatial and temporal sampling of atmospheric water vapor observations across Canada needs to be improved. A series of instruments and methods including a 940-nm solar absorption band radiometer (R) and radiosonde (S) analysis from a numerical weather prediction model and a ground-based bi-frequency Global Positioning System (GPS) were used to evaluate the integrated atmospheric water vapor (IWV) at various sites in Canada and Alaska from a multiyear database. The IWV-R measurements were collected within the framework of the North American Sun Radiometry network (AERONET/AEROCAN). Intercomparisons between [IWV-GPS and IWV-S], [IWV-R and IWV-GPS], and [IWV-R and IWV-S] show root mean square (RMS) differences of 1.8, 1.9, and 2.2 kg m � 2 , respectively. GPS meteorology appears to be the easiest approach to calibrate the solar radiometer water vapor band owing to its flexibility, and it allows us to overcome the Sun radiometry limitation in high-latitude areas like the Arctic. The sensitivity of the GPS retrieval to various parameters like GPS satellite constellation and meteorological data are discussed. The classical linear relationship between the surface temperature and the integrated weighted mean temperature profile needed for IWV-GPS retrieval may be significantly different for Arctic air masses compared with midlatitude air masses in the case of tropospheric temperature profile inversion. An ever-expanding multiyear (1994–2001) North American summer water vapor climatology, derived from AERONET/Canadian Sun Radiometer Network, is presented and analyzed, showing a mean value of 19.8 ± 6.1 kg m � 2 and variations from 17 kg m � 2 in Alaska to 23 kg m � 2 in southeastern Canada. The results in Bonanza Creek, Alaska, show significant interannual variations with a peak in 1997, which may

Downward longwave irradiance uncertainty under arctic atmospheres: Measurements and modeling

Abstract: [1] Measurement and modeling of downward longwave irradiance are a special challenge in arctic winter due to its low water vapor content and the extreme meteorological conditions. There are questions about the representativeness of the instrument calibration, the consistency and unfcertainty of measurements and models in these environments. The Second International Pyrgeometer and Absolute Sky-scanning Radiometer Comparison (IPASRC-II), which was conducted at Atmospheric Radiation Measurement (ARM) program's North Slope of Alaska (NSA) site in Barrow provided a unique opportunity to compare high accuracy downward longwave irradiance measurements and radiative transfer model computations during arctic winter. Participants from 11 international institutions deployed 14 pyrgeometers, which were field-calibrated against the Absolute Sky-scanning Radiometer (ASR). Continuous measurements over a 10-day period in early March 2001 with frequent clear-sky conditions yielded downward longwave irradiances between 120 and 240 W m−2. The small average difference between ASR irradiances, pyrgeometer measurements, MODTRAN and LBLRTM radiative transfer computations indicates that the absolute uncertainty of measured downward longwave irradiance under arctic winter conditions is within ±2 W m−2.

Comparisons of Line-of-Sight Water Vapor Observations Using the Global Positioning System and a Pointing Microwave Radiometer

Abstract: Line-of-sight measurements of integrated water vapor from a global positioning system (GPS) receiver and a microwave radiometer are compared. These two instruments were collocated at the central facility of the Department of Energy’s Atmospheric Radiation Measurement Program’s Southern Great Plains region, near Lamont, Oklahoma. The comparison was made using 47 days of observations in May and June of 2000. Weather conditions during this time period were variable with total integrated water vapor ranging from less than 10 to more than 50 mm. To minimize errors in the microwave radiometer observations, observations were compared during conditions when the liquid water measured by the radiometer was less than 0.1 mm. The linear correlation of the observations between the two instruments is 0.99 with a root-mean-square difference of the GPS water vapor to a linear fit of the microwave radiometer of 1.3 mm. The results from these comparisons are used to evaluate the ability of networks of GPS receivers to measure instantaneous line-of-sight integrals of water vapor. A discussion and analysis is provided regarding the additional information of the water vapor field contained in these observations compared to time- and space-averaged zenith and gradient measurements.

Airborne Sun photometer measurements of aerosol optical depth and columnar water vapor during the Puerto Rico Dust Experiment and comparison with land, aircraft, and satellite measurements

Abstract: Analyses of aerosol optical depth (AOD) and columnar water vapor (CWV) measurements obtained with the six-channel NASA Ames Airborne Tracking Sunphotometer (AATS-6) mounted on a twin-engine aircraft during the summer 2000 Puerto Rico Dust Experiment are presented. In general, aerosol extinction values calculated from AATS-6 AOD measurements acquired during aircraft profiles up to 5 km ASL reproduce the vertical structure measured by coincident aircraft in-situ measurements of total aerosol number and surface area concentration. Calculations show that the spectral dependence of AOD was small (mean Angstrom wavelength exponents of approximately 0.20) within three atmospheric layers defined as the total column beneath the top of each aircraft profile, the region beneath the trade wind inversion, and the region within the Saharan Air Layer (SAL) above the trade inversion. This spectral behavior is consistent with attenuation of incoming solar radiation by large dust particles or by dust plus sea salt. Values of CWV calculated from profile measurements by AATS-6 at 941.9 nm and from aircraft in-situ measurements by a chilled mirror dewpoint hygrometer agree to within approximately 4% (0.13 g/sq cm). AATS-6 AOD values measured on the ground at Roosevelt Roads Naval Air Station and during low altitude aircraft runs over the adjacent Cabras Island aerosol/radiation ground site agree to within 0.004 to 0.030 with coincident data obtained with an AERONET Sun/sky Cimel radiometer located at Cabras Island. For the same observation times, AERONET retrievals of CWV exceed AATS-6 values by a mean of 0.74 g/sq cm (approximately 21 %) for the 2.9-3.9 g/sq cm measured by AATS-6. Comparison of AATS-6 aerosol extinction values obtained during four aircraft ascents over Cabras Island with corresponding values calculated from coincident aerosol backscatter measurements by a ground-based micro-pulse lidar (MPL-Net) located at Cabras yields a similar vertical structure above the trade inversion. Finally, AATS-6 AOD values measured during low altitude aircraft traverses over the ocean are compared with corresponding AOD values retrieved over water from upwelling radiance measurements by the MODIS, TOMS, and GOES-8 Imager satellite sensors, with mixed results. These exercises highlight the need for continued satellite sensor comparison/validation studies to improve satellite AOD retrieval algorithms, and the usefulness of airborne sunphotometer measurements in the validation process.