Showing papers on "Radiometer published in 2011"

A Cross-calibrated, Multiplatform Ocean Surface Wind Velocity Product for Meteorological and Oceanographic Applications

Abstract: The ocean surface wind mediates exchanges between the ocean and the atmosphere. These air–sea exchange processes are critical for understanding and predicting atmosphere, ocean, and wave phenomena on many time and space scales. A cross-calibrated multiplatform (CCMP) long-term data record of satellite ocean surface winds is available from 1987 to 2008 with planned extensions through 2012. A variational analysis method (VAM) is used to combine surface wind data derived from conventional and in situ sources and multiple satellites into a consistent nearglobal analysis at 25-km resolution, every 6 h. The input data are cross-calibrated wind speeds derived from the Special Sensor Microwave Imager (SSM/I; F08–F15), the Tropical Rainfall Measuring Mission Microwave Imager (TMI), and the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), and wind vectors from SeaWinds on the NASA Quick Scatterometer (QuikSCAT) and on the second Japanese Advanced Earth Observing Satellite (ADEOS-...

ARCADE 2 MEASUREMENT OF THE ABSOLUTE SKY BRIGHTNESS AT 3-90 GHz

Abstract: The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the cosmic microwave background (CMB) temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an excess radio rise of 54 ± 6 mK at 3.3 GHz in addition to a CMB temperature of 2.731 ± 0.004 K. Combining the ARCADE 2 data with data from the literature shows an excess power-law spectrum of T = 24.1 ± 2. 1( K) (ν/ν0) −2.599±0.036 from 22 MHz to 10 GHz (ν0 = 310 MHz) in addition to a CMB temperature of 2.725 ± 0.001 K.

An Algorithm for Merging SMAP Radiometer and Radar Data for High-Resolution Soil-Moisture Retrieval

Abstract: A robust and simple algorithm is developed to merge L-band radiometer retrievals and L-band radar observations to obtain high-resolution (9-km) soil-moisture estimates from data of the NASA Soil Moisture Active and Passive (SMAP) mission. The algorithm exploits the established accuracy of coarse-scale radiometer soil-moisture retrievals and blends this with the fine-scale spatial heterogeneity detectable by radar observations to produce a high-resolution optimal soil-moisture estimate at 9 km. The capability of the algorithm is demonstrated by implementing the approach using the airborne Passive and Active L-band System (PALS) instrument data set from Soil Moisture Experiments 2002 (SMEX02) and a four-month synthetic data set in an Observation System Simulation Experiment (OSSE) framework. The results indicate that the algorithm has the potential to obtain better soil-moisture accuracy at a high resolution and show an improvement in root-mean-square error of 0.015-0.02-cm3/cm3 volumetric soil moisture over the minimum performance taken to be retrievals based on radiometer measurements resampled to a finer scale. These results are based on PALS data from SMEX02 and a four-month OSSE data set and need to be further confirmed for different hydroclimatic regions using airborne data sets from prelaunch calibration/validation field campaigns of the SMAP mission.

An Observationally Generated A Priori Database for Microwave Rainfall Retrievals

Abstract: The combination of active and passive microwave sensors on board the Tropical Rainfall Measuring Mission (TRMM) satellite have been used to construct observationally constrained databases of precipitation profiles for use in passive microwave rainfall retrieval algorithms over oceans. The method uses a very conservative approach that begins with the operational TRMM precipitation radar algorithm and adjusts its solution only as necessary to simultaneously match the radiometer observations. Where the TRMM precipitation radar (PR) indicates no rain, an optimal estimation procedure using TRMM Microwave Imager (TMI) radiances is used to retrieve nonraining parameters. The optimal estimation methodology ensures that the geophysical parameters are fully consistent with the observed radiances. Within raining fields of view, cloud-resolving model outputs are matched to the liquid and frozen hydrometeor profiles retrieved by the TRMM PR. The profiles constructed in this manner are subsequently used to com...

A new soil freeze/thaw discriminant algorithm using AMSR‐E passive microwave imagery

Abstract: The soil freeze–thaw controls the hydrological and carbon cycling and thus affects water and energy exchanges at land surface. This article reported a newly developed algorithm for distinguishing the freeze/thaw status of surface soil. The algorithm was based on information from Advanced Microwave Scanning Radiometer Enhanced (AMSR-E) which records brightness temperature (Tb) in the afternoon and after midnight. The criteria and discriminant functions were obtained from both radiometer observations and model simulations. First of all, the microwave radiation from freeze–thaw soil was examined by carrying out experimental measurements at 18·7 and 36·5 GHz using a Truck-mounted Multi-frequency Microwave Radiometer (TMMR) in the Heihe River of China. The experimental results showed that the soil moisture is a key component that differentiates the microwave radiation behaviours during the freeze–thaw process, and the differences in soil temperature and emissivity between frozen and thawed soils were found to be the most important criteria. Secondly, a combined model was developed to consider the impacts of complex ground surface conditions on the discrimination. The model simulations quite followed the trend of in situ observations with an overall relation coefficient (R) of approximately 0·88. Finally, the ratio of Tb18·7H (horizontally polarized Tb at 18·7 GHz) to Tb36·5V was considered primarily as the quasi-emissivity, which is more reasonable and explicit in measuring the microwave radiation changes in soil freezing and thawing than the spectral gradient. By combining Tb36·5V to indicate the soil temperature variety, a Fisher linear discrimination analysis was used to establish the discriminant functions. After being corrected by TMMR measurements, the new discriminant algorithm had an overall accuracy of 86% when validated by 4-cm soil temperature. The multi-year discriminant results also provided a good agreement with the classification map of frozen ground in China. Copyright © 2011 John Wiley & Sons, Ltd.

Error Estimates for Near-Real-Time Satellite Soil Moisture as Derived From the Land Parameter Retrieval Model

Abstract: A time-efficient solution to estimate the error of satellite surface soil moisture from the land parameter retrieval model is presented. The errors are estimated using an analytical solution for soil moisture retrievals from this radiative-transfer-based model that derives soil moisture from low-frequency passive microwave observations. The error estimate is based on a basic error propagation equation which uses the partial derivatives of the radiative transfer equation and estimated errors for each individual input parameter. Results similar to those of the Monte Carlo approach show that the developed time-efficient methodology could substitute computationally intensive methods. This procedure is therefore a welcome solution for near-real-time data assimilation studies where both the soil moisture product and error estimate are needed. The developed method is applied to the C-, X-, and Ku-bands of the Aqua/Advanced Microwave Scanning Radiometer for Earth Observing System sensor to study differences in errors between frequencies.

Observed Land–Atmosphere Coupling from Satellite Remote Sensing and Reanalysis

Abstract: The lack of observational data for use in evaluating the realism of model-based land–atmosphere feedback signal and strength has been deemed a major obstacle to future improvements to seasonal weather prediction by the Global Land–Atmosphere Coupling Experiment (GLACE). To address this need, a 7-yr (2002–09) satellite remote sensing data record is exploited to produce for the first time global maps of predominant coupling signals. Specifically, a previously implemented convective triggering potential (CTP)–humidity index (HI) framework for describing atmospheric controls on soil moisture–rainfall feedbacks is revisited and generalized for global application using CTP and HI from the Atmospheric Infrared Sounder (AIRS), soil moisture from the Advanced Microwave Scanning Radiometer for Earth Observing System (EOS) (AMSR-E), and the U.S. Climate Prediction Center (CPC) merged satellite rainfall product (CMORPH). Based on observations taken during an AMSR-E-derived convective rainfall season, the glob...

Water Vapor Continuum Absorption in the Microwave

Abstract: The accurate modeling of continuum absorption is crucial for the so-called window regions of the spectrum, the relatively transparent regions between lines. The window regions in the microwave are of critical importance for Earth remote sensing and data assimilation. Presented in this paper is an evaluation of the widely used Mlawer, Tobin, Clough, Kneizys, and Davis (MT_CKD) water vapor continuum model in the microwave region, performed using measurements from ground-based radiometers operated by the Department of Energy's Atmospheric Radiation Measurement Program at sites in Oklahoma, USA, and the Black Forest, Germany. The radiometers used were the Radiometrics 23.8/31.4-GHz microwave radiometers (MWRs), the Radiometer Physics GmbH 90/150-GHz MWR at high frequencies (MWRHF), and the Radiometrics 183 GHz G-band vapor radiometer profiler (GVRP). Radiometer measurements were compared with brightness temperatures calculated using radiosonde temperature and humidity profiles input to the monochromatic radiative transfer model (MonoRTM), which uses the MT_CKD continuum model. Measurements at 23.8 GHz were used to correct for biases in the total precipitable water vapor (PWV) from the radiosondes. The long-term 31.4 GHz data set, with a range of PWV values spanning from 0.15 to 5 cm, allowed the separation of uncertainties in the self- and foreign-broadened components of the water vapor continuum. The MT_CKD model has been updated in the microwave region to provide improved agreement with the measurements. MonoRTM has been updated accordingly. The results for the different instruments and frequencies were consistent, providing high confidence in the continuum updates. The estimated uncertainties on the updated continuum coefficients in MT_CKD are 4% on the foreign-broadened water vapor continuum and 4% on the self-broadened water vapor continuum.

The ARCADE 2 Instrument

Abstract: The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of the cosmic microwave background and Galactic and extragalactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes a double-nulled design where emission from the sky is compared to that from an external cryogenic full-aperture blackbody calibrator by cryogenic switching radiometers containing internal blackbody reference loads. In order to further minimize sources of systematic error, ARCADE 2 features a cold fully open aperture with all radiometrically active components maintained at near 2.7 K without windows or other warm objects, achieved through a novel thermal design. We discuss the design and performance of the ARCADE 2 instrument in its 2005 and 2006 flights.

Mapping Field-Scale Soil Moisture With L-Band Radiometer and Ground-Penetrating Radar Over Bare Soil

Abstract: Accurate estimates of surface soil moisture are essential in many research fields, including agriculture, hydrology, and meteorology. The objective of this study was to evaluate two remote-sensing methods for mapping the soil moisture of a bare soil, namely, L-band radiometry using brightness temperature and ground-penetrating radar (GPR) using surface reflection inversion. Invasive time-domain reflectometry (TDR) measurements were used as a reference. A field experiment was performed in which these three methods were used to map soil moisture after controlled heterogeneous irrigation that ensured a wide range of water content. The heterogeneous irrigation pattern was reasonably well reproduced by both remote-sensing techniques. However, significant differences in the absolute moisture values retrieved were observed. This discrepancy was attributed to different sensing depths and areas and different sensitivities to soil surface roughness. For GPR, the effect of roughness was excluded by operating at low frequencies (0.2-0.8 GHz) that were not sensitive to the field surface roughness. The root mean square (rms) error between soil moisture measured by GPR and TDR was 0.038 m3·m-3. For the radiometer, the rms error decreased from 0.062 (horizontal polarization) and 0.054 (vertical polarization) to 0.020 m3·m-3 (both polarizations) after accounting for roughness using an empirical model that required calibration with reference TDR measurements. Monte Carlo simulations showed that around 20% of the reference data were required to obtain a good roughness calibration for the entire field. It was concluded that relatively accurate measurements were possible with both methods, although accounting for surface roughness was essential for radiometry.

The High-Altitude MMIC Sounding Radiometer for the Global Hawk Unmanned Aerial Vehicle: Instrument Description and Performance

Abstract: The Jet Propulsion Laboratory's High-Altitude Monolithic Microwave Integrated Circuit (MMIC) Sounding Radiometer (HAMSR) is a 25-channel cross-track scanning microwave sounder with channels near the 60- and 118-GHz oxygen lines and the 183-GHz water-vapor line. It has previously participated in three hurricane field campaigns, namely, CAMEX-4 (2001), Tropical Cloud Systems and Processes (2005), and NASA African Monsoon Multidisciplinary Analyses (2006). The HAMSR instrument was recently extensively upgraded for the deployment on the Global Hawk (GH) unmanned aerial vehicle platform. One of the major upgrades is the addition of a front-end low-noise amplifier, developed by JPL, to the 183-GHz channel which reduces the noise in this channel to less than 0.1 K at the sensor resolution (~2 km). This will enable HAMSR to observe much smaller scale water-vapor features. Another major upgrade is an enhanced data system that provides onboard science processing capability and real-time data access. HAMSR has been well characterized, including passband characterization, along-scan bias characterization, and calibrated noise-performance characterization. The absolute calibration is determined in-flight and has been estimated to be better than 1.5 K from previous campaigns. In 2010, HAMSR participated in the NASA Genesis and Rapid Intensification Processes campaign on the GH to study tropical cyclone genesis and rapid intensification. HAMSR-derived products include observations of the atmospheric state through retrievals of temperature, water-vapor, and cloud-liquid-water profiles. Other products include convective intensity, precipitation content, and 3-D storm structure.

CAROLS: A New Airborne L-Band Radiometer for Ocean Surface and Land Observations

Abstract: The "Cooperative Airborne Radiometer for Ocean and Land Studies" (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer--STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity.

Measurements of high-frequency light fluctuations induced by sea surface waves with an Underwater Porcupine Radiometer System

Abstract: [1] Under clear skies the underwater light field within the near-surface ocean shows large fluctuations caused by focusing of sunlight by surface waves. The downwelling light at near-surface depths can fluctuate greatly on times scales as short as milliseconds and distances less than 1 cm. Specially designed radiometers and measurement strategies are required to adequately characterize these fluctuations. We developed an Underwater Porcupine Radiometer System which has a capability to measure light fluctuations with a sampling frequency of 1 kHz. This instrument is equipped with 23 radiometric sensors for measuring time series of the downward plane irradiance, Ed(t), at several light wavelengths λ and the downwelling radiance L(t) at λ = 532 nm for different zenith angles within two orthogonal azimuthal planes. We describe the critical components of the Porcupine instrument and measurement protocols, and present example results from measurements made at near-surface depths in the ocean. We show that the irradiance collector of a few millimeters in diameter or smaller is required to provide adequate measurement of light flashes produced by wave focusing. The measurements with larger irradiance collectors can result in deceptive reduction of the measured intensity of fluctuations. The brightest flashes of irradiance or radiance can exceed the time-averaged irradiance or radiance by an order of magnitude and the duration of flashes is typically on the order of milliseconds to tens of milliseconds. The intensity of light fluctuations decreases rapidly with depth and is higher at longer light wavelengths compared with shorter wavelengths within the visible spectral range.

Characterizing theFY-3AMicrowave Temperature Sounder Using the ECMWF Model

Abstract: China’s Feng-Yun-3A (FY-3A), launched in May 2008, is the first in a series of seven polar-orbiting meteorological satellites planned for the next decade by China. The FY-3 series is set to become an important data source for numerical weather prediction (NWP), reanalysis, and climate science. FY-3A is equipped with a microwave temperature sounding instrument (MWTS). This study reports an assessment of the MWTS instrument using the ECMWF NWP model, radiative transfer modeling, and comparisons with equivalent observations from the Advanced Microwave Sounding Unit-A (AMSU-A). The study suggests the MWTS instrument is affected by biases related to large shifts, or errors, in the frequency of the channel passbands as well as radiometer nonlinearity. The passband shifts, relative to prelaunch measurements, are 55, 39, and 33 MHz for channels 2–4, respectively. Relative to the design specification the shifts are 60, 80, and 83 MHz, with uncertainties of ±2.5 MHz. The radiometer nonlinearity results in a...

Algorithms to retrieve optical properties of three component aerosols from two-wavelength backscatter and one-wavelength polarization lidar measurements considering nonsphericity of dust

Abstract: We developed backward and forward types of algorithms for estimating the vertical profiles of extinction coefficients at 532 nm for three component aerosols (water-soluble, dust, and sea salt) using three-channel Mie-scattering lidar data of the backscatter (β) at 532 and 1064 nm and the depolarization ratio (δ) at 532 nm. While the water-soluble and sea-salt particles were reasonably assumed to be spherical, the dust particles were treated as randomly oriented spheroids to account for their nonsphericity. The introduction of spheroid models enabled us to more effectively use the three-channel data (i.e., 2β+1δ data) and to reduce the uncertainties caused by the assumption of spherical dust particles in our previously developed algorithms. We also performed an extensive sensitivity study to estimate retrieval errors, which showed that the errors in the extinction coefficient for each aerosol component were smaller than 30% (60%) for the backward (forward) algorithm when the measurement errors were ±5%. We demonstrated the ability of the algorithms to partition aerosol layers consisting of three aerosol components by applying them to shipborne lidar data. Comparisons with sky radiometer measurements revealed that the retrieved optical thickness and angstrom exponent of aerosols using the algorithms developed in this paper agreed well with the sky radiometer measurements (within 6%).

A spectral method for retrieving cloud optical thickness and effective radius from surface-based transmittance measurements

Abstract: . We introduce a new spectral method for the retrieval of optical thickness and effective radius from cloud transmittance that relies on the spectral slope of the normalized transmittance between 1565 nm and 1634 nm, and on cloud transmittance at a visible wavelength. The standard dual-wavelength technique, which is traditionally used in reflectance-based retrievals, is ill-suited for transmittance because it lacks sensitivity to effective radius, especially for optically thin clouds. Using the spectral slope rather than the transmittance itself enhances the sensitivity of transmittance observations with respect to the effective radius. This is demonstrated by applying it to the moderate spectral resolution observations from the Solar Spectral Flux Radiometer (SSFR) and Shortwave Spectroradiometer (SWS), and by examining the retrieval uncertainties of the standard and the spectral method for data from the DOE ARM Southern Great Plains (SGP) site and a NOAA ship cruise (ICEALOT). The liquid water path (LWP) is derived from the retrieved optical thickness and effective radius, based on two different assumptions about the cloud vertical profile, and compared to the simultaneous observations from a microwave radiometer. Optical thickness and effective radius is also compared to MODIS retrievals. In general, the effective radius uncertainties were much larger for the standard retrieval than for the spectral retrieval, particularly for thin clouds. When defining 2 μm as upper limit for the tolerable uncertainty of the effective radius, the standard method returned only very few valid retrievals for clouds with an optical thickness below 25. For the analyzed ICEALOT data (mean optical thickness 23), the spectral method provided valid retrievals for 84 % of the data (24 % for the standard method). For the SGP data (mean optical thickness 44), both methods provided a high return of 90 % for the spectral method and 78 % for the standard method.

Tropospheric Corrections for Coastal Altimetry

Abstract: The altimeter range should be corrected for tropospheric path delays due to atmospheric pressure at sea level and atmospheric humidity. Over open ocean, these corrections are performed with enough accuracy using the microwave radiometer for the wet path delay and meteorological model analyses for the dry path delay. In coastal areas, specific studies are needed to assess the quality of the standard products and to propose specific processing if necessary. For the wet tropospheric correction, new promising approaches are presented based on optimal combination of radiometer, meteorological model, GNSS and land information. For the dry tropospheric correction, an assessment of the accuracy of the model-based estimation is provided.

Design of medical radiometer front-end for improved performance

Abstract: We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25-3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (< 5 mm × 5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure.Numerical simulations were performed to test the design concepts before building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with a low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.

Atmospheric observations of multiple molecular species using ultra-high-resolution external cavity quantum cascade laser heterodyne radiometry

Abstract: We demonstrate a widely tunable laser heterodyne radiometer operating in the thermal IR during an atmospheric observation campaign in the solar occultation viewing mode. An external cavity quantum cascade laser tunable within a range of 1120 to 1238 cm−1 is used as the local oscillator (LO) of the instrument. Ultra-high-resolution (60 MHz or 0.002 cm−1) transmission spectroscopy of several atmospheric species (water vapor, ozone, nitrous oxide, methane, and dichlorodifluoromethane) has been demonstrated within four precisely selected molecule-specific narrow spectral windows (∼1 cm−1). Atmospheric transmission lines within each selected window were fully resolved through mode-hop-free continuous tuning of the LO frequency. Comparison measurements were made simultaneously with a high-resolution Fourier transform spectrometer to demonstrate the advantages of the laser heterodyne system for atmospheric sounding at high spectral and spatial resolutions.

Directional radiometry and radiative transfer: A new paradigm

Abstract: Measurements with directional radiometers and calculations based on the radiative transfer equation (RTE) have been at the very heart of weather and climate modeling and terrestrial remote sensing. The quantification of the energy budget of the Earth's climate system requires exquisite measurements and computations of the incoming and outgoing electromagnetic energy, while global characterization of climate system's components relies heavily on theoretical inversions of observational data obtained with various passive and active instruments. The same basic problems involving electromagnetic energy transport and its use for diagnostic and characterization purposes are encountered in numerous other areas of science, biomedicine, and engineering. Yet both the discipline of directional radiometry and the radiative transfer theory (RTT) have traditionally been based on phenomenological concepts many of which turn out to be profound misconceptions. Contrary to the widespread belief, a collimated radiometer does not, in general, measure the flow of electromagnetic energy along its optical axis, while the specific intensity does not quantify the amount of electromagnetic energy transported in a given direction. The recently developed microphysical approach to radiative transfer and directional radiometry is explicitly based on the Maxwell equations and clarifies the physical nature of measurements with collimated radiometers and the actual content of the RTE. It reveals that the specific intensity has no fundamental physical meaning besides being a mathematical solution of the RTE, while the RTE itself is nothing more than an intermediate auxiliary equation. Only under special circumstances detailed in this review can the solution of the RTE be used to compute the time-averaged local Poynting vector as well as be measured by a collimated radiometer. These firmly established facts make the combination of the RTE and a collimated radiometer useful in a well-defined range of applications. However, outside the domain of validity of the RTT the practical usefulness of measurements with collimated radiometers remains uncertain, while the theoretical modeling of these measurements and the solution of the energy-budget problem require a more sophisticated approach than solving the RTE.

Radiometer and Profiler Analysis of the Effects of a Bore and a Solitary Wave on the Stability of the Nocturnal Boundary Layer

Abstract: This study uses data from a microwave profiling radiometer (MPR), along with 915-MHz wind profiler, Doppler radar, and surface data to quantify the kinematic and thermodynamic effects of two wave features, an undular bore and a soliton, on the nocturnal boundary layer (NBL) at high temporal resolution. Both wave features passed directly over the MPR and the wind profiler, allowing for detailed analyses. The effects of the wave features on the convective environment are examined, and convective initiation (CI) associated with the wave features is discussed. The undular bore was illustrated well in Doppler velocity data, and profiler measurements indicated that it produced four wavelengths of upward and downward motion. MPR-derived time–height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer, along with a decrease in stability, partially associated with mixing of the NBL. The soliton produced a temporary decrease in the depth of the NBL...

A Modular Optimal Estimation Method for Combined Radar–Radiometer Precipitation Profiling

Abstract: Although zonal mean rain rates from the Tropical Rainfall Measuring Mission (TRMM) are in good ( 10%) biases of differing sign at various GV locations. Reducing these biases is important in the context of developing a database of cloud profiles for passive microwave retrievals that is based upon the PR-measured profiles. A retrieval framework based upon optimal estimation theory is proposed wherein three parameters describing the raindrop size distribution (DSD), ice particle size distribution, and cloud water path (cLWP) are retrieved for each radar profile. The modular nature of the framework provides the opportunity to test the sensitivity of the retrieval to the inclu...

Low optical power reference detector implemented in the validation of two independent techniques for calibrating photon-counting detectors.

Abstract: We introduce a technique for measuring detection efficiency that is traceable to the primary standard, the cryogenic radiometer, through a reference silicon photodiode trap detector. The trap detector, used in conjunction with a switched integrator amplifier, can measure signals down to the 0.1 pW (3 x 10⁵ photons second-1) level with 0.1% uncertainty in a total integration time of 300 seconds. This provides a convenient calibration standard for measurements at these levels across the optical spectrum (UV - near IR). A second technique is also described, based on correlated photons produced via parametric down-conversion. This can be used to directly measure detection efficiency in the photon counting regime, and provides a route for expanding the formulation of the candela in terms of photon flux to enable it to address the needs of emerging quantum optical technologies and applications. The two independent techniques were cross-validated by a comparison carried out at 702.2 nm, which showed agreement to within 0.2%.

NPP VIIRS Geometric Performance Status

Abstract: Visible Infrared Imager Radiometer Suite (VIIRS) instrument on-board the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project (NPP) satellite is scheduled for launch in October, 2011 It is to provide satellite measured radiance/reflectance data for both weather and climate applications Along with radiometric calibration, geometric characterization and calibration of Sensor Data Records (SDRs) are crucial to the VIIRS Environmental Data Record (EDR) algorithms and products which are used in numerical weather prediction (NWP) The instrument geometric performance includes: 1) sensor (detector) spatial response, parameterized by the dynamic field of view (DFOV) in the scan direction and instantaneous FOV (IFOV) in the track direction, modulation transfer function (MTF) for the 17 moderate resolution bands (M-bands), and horizontal spatial resolution (HSR) for the five imagery bands (I-bands); 2) matrices of band-to-band co-registration (BBR) from the corresponding detectors in all band pairs; and 3) pointing knowledge and stability characteristics that includes scan plane tilt, scan rate and scan start position variations, and thermally induced variations in pointing with respect to orbital position They have been calibrated and characterized through ground testing under ambient and thermal vacuum conditions, numerical modeling and analysis This paper summarizes the results, which are in general compliance with specifications, along with anomaly investigations, and describes paths forward for characterizing on-orbit BBR and spatial response, and for improving instrument on-orbit performance in pointing and geolocation

Deployment of a Tethered-Balloon System for Microphysics and Radiative Measurements in Mixed-Phase Clouds at Ny-Ålesund and South Pole

Abstract: A tethered-balloon system capable of making microphysical and radiative measurements in clouds is describedandexamplesofmeasurementsinboundarylayerstratuscloudsintheArcticandattheSouthPoleare presented. A 43-m 3 helium-filled balloon lofts an instrument package that is powered by two copper conductors in the tether. The instrument package can support several instruments, including, but not limited to, a cloud particle imager; a forward-scattering spectrometer probe; temperature, pressure, humidity, and wind sensors; ice nuclei filters; and a 4-p radiometer that measures actinic flux at 500 and 800 nm. The balloon can stay aloft for an extended period of time (in excess of 24 h) and conduct vertical profiles up to about 1‐2 km, contingent upon payload weight, wind speed, and surface elevation. Examples of measurements in mixed