M. Klein

University of Colorado, Denver, Colorado, United States

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Publications (48)33.43 Total impact

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    ABSTRACT: Measurement of water vapor and cloud liquid during very cold (-20 to -40 Deg. C) and dry (precipitable water vapor < 5 mm) conditions is a very important, but difficult task. Starting in 1999, three radiometric experiments were conducted at the U. S. Department of Energypsilas Atmospheric Radiation Measurement (ARM) Programpsilas North Slope of Alaska (NSA) field site near Barrow, Alaska. Principal results from the first two experiments are summarized. Most recently, the Radiative Heating in Underexplored Bands Campaign (RHUBC) was conducted in February-March 2007. The millimeter- and submillimeter-wave channels of the ground-based scanning radiometer (GSR) are very sensitive to low water vapor and cloud contents and allow for accurate observations in the extremely dry and cold conditions typical of the Arctic. Moreover, window channels (e.g., at 90 and 340 GHz, both with horizontal and vertical polarizations) show a high sensitivity to Artic clouds over an extended range of liquid water path (LWP). For RHUBC, during conditions when the precipitable water vapor (PWV) was less than 2 mm, these radiometers were supplemented by frequent Vaisala RS92 radiosonde observations at the ARM site. In this paper, representative PWV and LWP retrievals from the GSR and several ARM instruments are compared. Based on comparisons with 87 RS92 RAOB launches, GSR PWV retrievals achieved almost unprecedented accuracy of 0.1 mm, or about 6 % of the mean PWV during the operating period.
    Microwave Radiometry and Remote Sensing of the Environment, 2008. MICRORAD 2008; 04/2008
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    ABSTRACT: A One Dimentional Variational (1DVAR) retrieval technique has been developed for obtaining temperature and humidity profiles from observations of the Ground-based Scanning Radiometer (GSR) operating at millimeter and submillimeter waves. The GSR participated in two Arctic experiments held at the Atmospheric Radiation Measurement (ARM) Program in Barrow, Alaska: the Water Vapor Intensive Operational Period (WVIOP, March-April 2004) and the Radiative Heating in Underexplored Bands Campaign (RHUBC, February-March 2007); data from both experiments are used in this paper. Temperature and humidity profiles retrieved with the 1DVAR technique are compared with simultaneous radiosonde observations. Examples and statistical results are presented and discussed to demonstrate the achieved retrieval accuracy and vertical resolution.
    Microwave Radiometry and Remote Sensing of the Environment, 2008. MICRORAD 2008; 04/2008
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    ABSTRACT: An unresolved issue in global soil moisture retrieval using passive microwave sensors is the spatial integration of heterogeneous landscape features to the nominal 50 km footprint observed by most low frequency satellite systems. One of the objectives of the Soil Moisture Experiments 2004 (SMEX04) was to address some aspects of this problem, specifically variability introduced by vegetation, topography and convective precipitation. Other goals included supporting the development of soil moisture data sets that would contribute to understanding the role of the land surface in the concurrent North American Monsoon System. SMEX04 was conducted over two regions: Arizona — semi-arid climate with sparse vegetation and moderate topography, and Sonora (Mexico) — moderate vegetation with strong topographic gradients. The Polarimetric Scanning Radiometer (PSR/CX) was flown on a Naval Research Lab P-3B aircraft as part of SMEX04 (10 dates of coverage over Arizona and 11 over Sonora). Radio Frequency Interference (RFI) was observed in both PSR and satellite-based (AMSR-E) observations at 6.92 GHz over Arizona, but no detectable RFI was observed over the Sonora domain. The PSR estimated soil moisture was in agreement with the ground-based estimates of soil moisture over both domains. The estimated error over the Sonora domain (SEE = 0.021 cm3/cm3) was higher than over the Arizona domain (SEE = 0.014 cm3/cm3). These results show the possibility of estimating soil moisture in areas of moderate and heterogeneous vegetation and high topographic variability.
    Remote Sensing of Environment. 01/2008;
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    ABSTRACT: In a recent paper by Mattioli et al., a significant difference was observed between upper-tropospheric and lower-stratospheric water vapor profiles as observed by two radiosonde systems operating in the Arctic. The first was the Vaisala RS90 system as operated by the U.S. Department of Energy's Atmospheric Radiation Measurement Program; the second was the operational radiosondes launched by the U.S. National Weather Service that used the Sippican VIZ-B2 type. Observations of precipitable water vapor by ground-based microwave radiometers and GPS did not reveal these differences. However, both the microwave radiometer profiler (MWRP) and the ground-based scanning radiometer (GSR) contain channels that receive a sig- nificant response from the upper-tropospheric region. In this paper, it is shown that brightness temperature (Tb) observations from these instruments are in consistent agreement with calculations based on the RS90 data but differ by several degrees with calculations based on the VIZ radiosondes. It is also shown that calculations of Tb can serve as a gross quality control of upper-tropospheric soundings.
    Journal of Atmospheric and Oceanic Technology - J ATMOS OCEAN TECHNOL. 01/2008; 25(10).
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    ABSTRACT: Measurements of water vapor and clouds in the polar regions are difficult, because conventional instruments show little sensitivity (~1.3 K/mm) to low amounts. On the other hand, millimeter- and submillimeter-wavelength radiometry offers greatly enhanced sensitivity (up to 51.4 K/mm, depending upon frequency). For this reason, the National Oceanic and Atmospheric Administration's Physical Science Division designed a new instrument, the Ground-Based Scanning Radiometer (GSR), for continuous and unattended observations at millimeter and submillimeter wavelengths (50-380 GHz). The GSR was deployed for the first time during the Arctic winter radiometric experiment in March-April 2004. In this paper, we discuss the GSR calibration procedure, which allows for accurate measurements during clear and cloudy skies. Error-budget analysis and comparison with independent measurements show an absolute accuracy on the order of 1-2 K. Examples of multifrequency and multiangle GSR observations are illustrated, representing a valuable new data set for the study of water vapor, clouds, and atmospheric absorption models in the Arctic.
    IEEE Transactions on Geoscience and Remote Sensing 10/2007; · 3.47 Impact Factor
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    ABSTRACT: The University of Colorado (CU) Center for Environmental Technology (CET) has developed a Ground- Based Scanning Radiometer (GSR) and deployed it during two important Arctic Experiments relevant to climate research. The first was the Arctic Winter Radiometric Experiment during March-April 2004 and the second was the Radiative Heating in Underexplored Bands Campaign (RHUBC) in February-March 2007. This paper summarizes some of the design details of the instrument and gives new results from both campaigns
    Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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    ABSTRACT: Ground-based observations at millimeter (mm) and submillimeter (submm) wavelengths were collected at the atmospheric radiation measurement program site at Barrow, AK, during the Arctic winter by a new 25-channel radiometer. A weighting function analysis is presented to demonstrate the enhanced sensitivity of mm- and submm-wave (50-400 GHz) radiometers to low vapor and liquid water contents with respect to conventional instruments such as the ones operating at centimeter (cm) wavelengths (20-30 GHz). In addition, based on measurements, we carried out a quantitative analysis of mm- and submm-wavelength sensitivity, yielding improvement factors from 1.5 to 69 for precipitable water vapor (PWV) and 3 to 4 for liquid water path (LWP) when compared to 20-30 GHz radiometers. Furthermore, using a simulated data set, we evaluate the effect of hydrometeor scattering: given the conditions occurring during the experiment, the scattering contribution is within the instrumental noise for most, but not all, of the considered channels. With the same data set, we demonstrate that in the dry conditions of the Arctic, a simple linear regression yields satisfactory results when applied on selected mm- and submm-wave channels. For a dual-channel combination, the expected accuracy is ~0.23 (0.007) mm for PWV (LWP), when using mm- and submm-wavelengths, whereas it is 0.37 (0.012) mm using cm-wave channels. When the retrieval is applied to real observations, the accuracy is found in agreement with theoretical expectations.
    IEEE Transactions on Geoscience and Remote Sensing 08/2007; · 3.47 Impact Factor
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    ABSTRACT: Six successful flights with the NASA P-3B aircraft over the Alaskan Arctic were conducted between March 18 and March 25, 2006 as part of the EOS Aqua AMSR-E sea ice validation efforts. The prime objective was to validate and evaluate AMSR-E snow depth on sea ice retrievals. A secondary objective was to underfly ICESat to assess the impact of snow on ICESat ice thickness retrievals. The NASA aircraft was equipped with four primary instruments: a microwave radiometer with frequencies similar to the AMSR-E, a snow depth radar, a radar altimeter, and a laser altimeter. Snow depth on sea ice validation was done in a two-step upscaling process: First, in-situ measurements of snow and sea ice along two transects were carried out over the Arctic Ocean adjacent to Barrow, AK and these measurements were overflown with the aircraft in order to validate the aircraft instruments. Subsequently, patterns over the Arctic Ocean corresponding to 4x8 12.5 km AMSR-E pixels were flown for direct comparison with the AMSR-E snow depth retrievals as well as along an ICESat track. The data set collected is probably the most comprehensive and extensive coincident set of surface- and aircraft-based ice thickness and snow depth measurements so far, and should prove useful for a variety of studies.
    AGU Fall Meeting Abstracts. 12/2006;
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    ABSTRACT: Accurate knowledge of snow-depth distribution over sea ice is critical for polar climate studies. Current snow-depth-over-sea-ice retrieval algorithms do not sufficiently account for variations in snow and ice physical properties that can affect the accuracy of retrievals. For this reason, airborne microwave observations were coordinated with ground-based measurements of snow depth and snow properties in the vicinity of Barrow, AK, in March 2003. In this paper, the effects of snowpack properties and ice conditions on microwave signatures are examined using detailed surface-based measurements and airborne observations in conjunction with a thermal microwave-emission model. A comparison of the Microwave Emission Model of Layered Snowpacks (MEMLS) simulations with detailed snowpack and ice data from stakes along the Elson Lagoon and the Beaufort Sea and radiometer data taken from low-level flights using a Polarimetric Scanning Radiometer (PSR-A) shows that MEMLS can be used to simulate snow on sea ice and is a useful tool for understanding the limitations of the snow-depth algorithm. Analysis of radiance data taken over the Elson Lagoon and the Beaufort Sea using MEMLS suggests that the radiometric differences between the two locations are due to the differences in sea-ice emissivity. Furthermore, measured brightness temperatures suggest that the current snow-depth retrieval algorithm is sufficient for areas of smooth first-year sea ice, whereas new algorithm coefficients are needed for rough first-year sea ice. Snowpack grain size and density remain an unresolved issue for snow-depth retrievals using passive-microwave radiances
    IEEE Transactions on Geoscience and Remote Sensing 12/2006; · 3.47 Impact Factor
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    ABSTRACT: Part of the Earth Observing System Aqua Advanced Microwave Scanning Radiometer (AMSR-E) Arctic sea ice validation campaign in March 2003 was dedicated to the validation of snow depth on sea ice and ice temperature products. The difficulty with validating these two variables is that neither can currently be measured other than in situ. For this reason, two aircraft flights on March 13 and 19, 2003, were dedicated to these products, and flight lines were coordinated with in situ measurements of snow and sea ice physical properties. One flight was in the vicinity of Barrow, AK, covering Elson Lagoon and the adjacent Chukchi and Beaufort Seas. The other flight was farther north in the Beaufort Sea (about 73degN, 147.5degW) and was coordinated with a Navy ice camp. The results confirm the AMSR-E snow depth algorithm and its coefficients for first-year ice when it is relatively smooth. For rough first-year ice and for multiyear ice, there is still a relationship between the spectral gradient ratio of 19 and 37 GHz, but a different set of algorithm coefficients is necessary. Comparisons using other AMSR-E channels did not provide a clear signature of sea ice characteristics and, hence, could not provide guidance for the choice of algorithm coefficients. The limited comparison of in situ snow-ice interface and surface temperatures with 6-GHz brightness temperatures, which are used for the retrieval of ice temperature, shows that the 6-GHz temperature is correlated with the snow-ice interface temperature to only a limited extent. For strong temperature gradients within the snow layer, it is clear that the 6-GHz temperature is a weighted average of the entire snow layer
    IEEE Transactions on Geoscience and Remote Sensing 12/2006; · 3.47 Impact Factor
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    ABSTRACT: Aircraft-acquired passive microwave data, laser radar height observations, RADARSAT synthetic aperture radar imagery, and in situ measurements obtained during the AMSR-Ice03 experiment are used to investigate relationships between microwave emission and ice characteristics over several space scales. The data fusion allows delineation of the shore-fast ice and pack ice in the Barrow area, AK, into several ice classes. Results show good agreement between observed and Polarimetric Scanning Radiometer (PSR)-derived snow depths over relatively smooth ice, with larger differences over ridged and rubbled ice. The PSR results are consistent with the effects on snow depth of the spatial distribution and nature of ice roughness, ridging, and other factors such as ice age. Apparent relationships exist between ice roughness and the degree of depolarization of emission at 10, 19, and 37 GHz. This depolarization would yield overestimates of total ice concentration using polarization-based algorithms, with indications of this seen when the NT-2 algorithm is applied to the PSR data. Other characteristics of the microwave data, such as effects of grounding of sea ice and large contrast between sea ice and adjacent land, are also apparent in the PSR data. Overall, the results further demonstrate the importance of macroscale ice roughness conditions such as ridging and rubbling on snow depth and microwave emissivity
    IEEE Transactions on Geoscience and Remote Sensing 12/2006; · 3.47 Impact Factor
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    ABSTRACT: First Page of the Article
    Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on; 09/2006
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    ABSTRACT: Corruption of C-band microwave brightness observations by radio-frequency interference (RFI) has been reported in recent data from orbiting radiometers; methods for mitigating these effects are of great importance for the design of future spaceborne microwave radiometers. One approach that has been suggested involves the use of multiple subchannels at C-band as opposed to a single channel; the use of multiple subchannels allows RFI to be detected and mitigated by analyzing relationships among subchannel brightnesses. While this approach has been utilized in previous airborne measurements, demonstrations of the RFI mitigation performance achieved have been difficult to obtain. To address this issue, an enhanced airborne system for observing radio-frequency interference effects on C-band microwave radiometers was developed, and is described in this paper. The system includes a traditional microwave radiometer with four C-band subchannels, so that RFI removal is possible using a subchannel mitigation algorithm. In addition, the system includes a digital receiver with the capability of providing high temporal and spectral resolution observations of interference. This high-resolution data allows improved understanding of RFI sources to be obtained, and also allows analysis of subchannel mitigation algorithm performance. Observations using the system in a test flight near Wallops Island, VA are described. Results show the four subchannel approach generally to be effective in mitigating the observed RFI sources, although examples are also illustrated using the digital receiver data to demonstrate failure of this approach. While studies of the digital receiver data alone could be performed to demonstrate further improvements in RFI mitigation, issues with this initial dataset limit the extent of such studies. Nevertheless, the results obtained still demonstrate qualitatively the improved RFI mitigation that can be achieved in brightness observations through the use of digit- - al receivers
    IEEE Transactions on Geoscience and Remote Sensing 08/2006; · 3.47 Impact Factor
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    ABSTRACT: An intensive operating period (IOP) was conducted at the U. S. Department of Energy's atmospheric radiation measurement (ARM) program's field site near Barrow, Alaska, during March 9 to April 9 2004. During this IOP, radiometers were deployed over a broad frequency range (22.235 to 380 GHz), including several channels near the strong water vapor absorption line at 183.31 GHz. These radiometers were supplemented by 4-times-a-day observations by Vaisala RS90 radiosondes at the ARM Duplex in Barrow, 8 dual-radiosonde launches with "Snow White" chilled mirror radiosondes at the same location, once daily Vaisala RS90 radiosondes launched at the ARM primary field site, and twice-daily synoptic launches by the US National Weather Service. Radiometers deployed included the ground-based scanning radiometer of NOAA (several frequencies from 50 to 380 GHz), the microwave radiometer and the radiometric profiler of ARM (frequencies from 22.235 to 60 GHz), and a global positioning system operated by NOAA. In addition, all of the ARM active cloud sensors were operated. Selected results from this experiment are presented, including observed radiometric sensitivities to precipitable water vapor and liquid water path, radiosonde comparisons between radiosondes types and to MWRP measurements, and a preliminary comparison of forward models with GSR data
    IEEE MicroRad, 2006; 02/2006
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    ABSTRACT: Not Available
    Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International; 08/2005
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    ABSTRACT: Not Available
    Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International; 08/2005
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    ABSTRACT: The Polarimetric Scanning Radiometer (PSR/CX) was flown on a P-3B aircraft as part of SMEX04. PSR/CX has been successfully operated during several previous airborne campaigns. The primary objectives of PSR/CX during SMEX04 are: 1) Contribute to the calibration and validation of AMSR observations over different parts of the globe and to check for the presence of Radio Frequency Interference (RFI), 2) Explore the potential for the development of soil moisture retrieval algorithms using C-band imagery in diverse landscapes (Arizona and Sonora, Mexico), and 3) to develop retrieval algorithms to estimate soil moisture over areas of topographic variability and vegetation. The dominant landuse classes in the different SMEX04 domains are: 1) Arizona - semi-arid climate with sparse vegetation and moderate topography, and 2) Sonora, Mexico - moderate vegetation with strong topographic gradients. SMEX04 consisted of about 84 flightlines at high altitude resulting in 21 mapping domains flown during August, 2004 (11 over Arizona and 10 over Sonora). Each mapping domain is about 75 km x 50 km, providing an excellent area for calibration and validation of AMSR-E observations. Some areas of the SMEX04 domain received heavy localized precipitation as a result of convective activity during the experiment. These resulted in interesting brightness temperature patterns with strong brightness temperature gradients. The presence of these diverse conditions will help address questions relating to scaling of spaceborne microwave observations. Results of comparison between PSR and AMSR and the use of microwave remote sensing to estimate soil moisture over wide range of vegetation and soil moisture conditions are also presented.
    AGU Spring Meeting Abstracts. 05/2005;
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    ABSTRACT: The 2004 Arctic Winter Radiometric Experiment was conducted at the North Slope of Alaska (NSA) Atmospheric Radiation Measurement (ARM) Program field site near Barrow, Alaska from March 9 to April 9, 2004. The goals of the experiment were: to study the microwave and millimeter wave radiometric response to water vapor and clouds during cold and dry conditions; to obtain data for forward model studies at frequencies ranging from 22.235 to 400 GHz, to demonstrate new Environmental Technology Laboratory's (ETL) radiometric receiver and calibration technology and to compare both radiometric and in situ measurements of water vapor.
    01/2005;
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    ABSTRACT: One of the main goals of the NASA Cold Land Processes Experiment is to explore scaling issues associated with microwave remote sensing of snow-packs. During the experiment, microwave radiometer observations were made at scales from the plot scale up to satellite pixels (25x25 Km2). In this paper, brightness temperatures acquired by the University of Tokyo's Ground Based Microwave Radiometer-7 (GBMR-7), the NOAA Polarimetric Scanning Radiometer (PSR/A), the SSM/I and AMSR-E satellite radiometers during the third Intensive Observation Period (IOP3, dry snow, February 19 - 25, 2003) have been analyzed and compared. Differences among observations are discussed. The effects of topography, as well as different antenna footprint positions, observation times and calibrations are considered and used to understand the differences observed at the different scales. In addition, inter-satellite differences were observed.
    AGU Fall Meeting Abstracts. 12/2004;
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    ABSTRACT: A multiinstrument radiometric experiment was conducted on the North Slope of Alaska near Barrow, Alaska, during March 9 to April 9 2004. Initial radiometric and radiosonde data from this experiment are presented.
    Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International; 10/2004

Publication Stats

349 Citations
33.43 Total Impact Points

Institutions

  • 2008
    • University of Colorado
      Denver, Colorado, United States
    • Università degli Studi dell'Aquila
      Aquila, Abruzzo, Italy
  • 2004
    • The Ohio State University
      • Department of Electrical and Computer Engineering
      Columbus, OH, United States
  • 2001–2003
    • University of Colorado at Boulder
      • Cooperative Institute for Research in Environmental Sciences (CIRES)
      Boulder, Colorado, United States
  • 2000
    • National Oceanic and Atmospheric Administration
      Boulder, Colorado, United States