Testbed Site Research Articles

초분광 항공원격탐사 테스트베드 구축 및 시험자료 획득

분광 영상의 효과적인 테스트베드 구축은 초분광 영상의 다양한 활용을 위하여 선행되어야한다. 본 연구에서는 다양한 연구 분야에 적용할 수 있는 테스트베드의 구축 방법 및 효용성에 대한 기초 연구를 수행하였다. 이를 위하여, 기존의 국내 외 테스트베드 생성 방법을 분석하고, 이를 바탕으로 하여 항공기 기반 초분광 센서의 촬영을 위한 테스트베드를 설계하였다. 구축된 테스트베드를 촬영한 영상에서 기준자료를 생성시키기 위하여, 본 연구에서는 대리보정에 의한 전처리 기법을 적용하고, 이에 대한 효용성을 분석하였다. 실험결과, 대리보정은 타프를 이용하는 것이 가장 이상적이지만, 상황에 따라서 분광반사율이 일정하거나, 변화폭이 상대적으로 적은 물질을 이용하는 것이 가능하다는 것을 확인하였다. 본 연구에서 촬영한 테스트베드 자료는 국내 외의 초분광 영상 처리 연구에 참조자료로 사용될 수 있을 것으로 사료된다. The construction of hyperspectral test-bed dataset is essential for the effective performance of hyperspectral image for various applications. In this study, we analyzed the technical points for generating of optimal hyperspectral test-bed site for hyperspectral sensors and the efficiency of hyperspectral test-bed site. In this regard regions we analyzed existing construction techniques for generating test-bed site in domestic and foreign, and designed the test-bed site to acquire images from the airborne hyperspectral sensor. To produce a reference data from the image of constructed test-bed site, this study applied vicarious correction as a pre-processing and analyzed its efficiency. The result presented that it was ideal to use tarp for the vicarious correction, but it is possible to use the materials with constant spectral reflectance or with relatively low variance of spectral reflectance. The test-bed data taken in this study can be employed as the reference of domestic and foreign studies for hyperspectral image processing.

A Flexible and Scalable Cooperative Surveillance Technique Using Integrated Ontology Reasoning

In large-scale smart camera networks, cooperation among devices is required for continuous tracking of targets and higher level reasoning. A large amount of multimedia data with derived metadata is generated and transferred among devices. In this paper, we design a large-scale surveillance system which consists of smart cameras. It complies with the standard specification to ensure interoperability among cameras and flexibility regarding integration of new devices and services. Surveillance data contained in them is integrated and structured according to the ontology, and useful context information can be derived. This paper introduces how to build surveillance knowledge base, import relevant data from other devices, and annotate data on interoperable framework which accommodates to the standard. The annotation process provides an impetus to the improvement of knowledge over time. We define a representative reasoning architecture that provides location-based context induction, and implemented in our test bed site to show superiority in large-scale surveillance.

Comparative Study on Mobile Wireless Sensor Network Testbeds

battery power of nodes and nodes automatically move to the docking station if the power drops below a certain threshold. Secondly, for outdoor testbeds, the solar panels can be used to auto-recharge the batteries. Thirdly, for localization the centralized or distributed mechanisms can be employed and finally, an interface is required so that the user can perform the experiment using testbed interface. The existing of most of the MWSNTs are the on the site interfaces which means the are located at the testbed site and cannot be accessed remotely. However, most of the static WSN testbeds provideremote, online interface, such as Quri Nettestbed (2). Several initiatives are already taken to address the above mentioned challenges, in the development of various testbeds. A few ofsuch testbeds are included in this paper in order to give an idea about the kind of workalready done and what are the future trends in research. The rest of the paper is organized as follows. In Section II, a brief study of testbeds for different selected parameters (such as infrastructure, deployment, mobility, auto-recharging, localization, collision, cost, and user interface) is presented. In Section III, a quantitative and qualitative comparison of selected testbeds is shown in tabular form. Section IV concludes the paper, highlighting current trends and a few suggestions for future work in development of MWSNTs.

A new joint application of non-invasive remote sensing techniques for structural health monitoring

This paper aims at analysing the potentialities of a new technological approach for the dynamic monitoring of civil infrastructures. The proposed approach is based on the joint use of a high-frequency thermal camera and a microwave radar interferometer to measure the oscillations due to traffic excitations of the Sihlhochstrasse Bridge, Switzerland, which was selected as test bed site in the ISTIMES project (EU—Seventh Framework Programme). The good quality of the results encourages the use of the proposed approach for the static and dynamic investigation of structures and infrastructures. Moreover, the remote sensing character of the two applied techniques makes them particularly suitable to study structures located in areas affected by natural hazard phenomena, and also to monitor cultural heritage buildings for which some conventional techniques are considered invasive. Obviously, their reliability needs further experiments and comparisons with standard contact sensors.

An investigation of correlation factors linking footing resistance on sand with cone penetration test results

Significant research effort has led to improvements in our ability to estimate the ultimate bearing resistance of footings in sand. These techniques often estimate the footing resistance at relatively large displacements, typically 10% of the footing width, qb0.1. Cone Penetration Test (CPT) design methods typically link qb0.1 and qc through a constant reduction factor, α. A range of α factors for shallow footings have been proposed, some methods suggest that α is constant and while others that it varies with footing width and depth (or stress level). There is a dearth of field data with which to compare these correlation factors, in particular where foundation width and depth have been varied in the same ground conditions. For this reason finite element analyses have proven to be a useful tool for performing the parametric studies required to asses factors controlling α. This paper describes the results of numerical analyses performed to investigate α factors for soil profiles which were calibrated using the results of the CPT tests performed at a dense sand test-bed site. The numerical model was first used to perform parametric analyses to consider the effect of footing width, B and footing depth, D on the α factor mobilised in dense Blessington sand. In order to assess the effects of relative density, footing tests in a range of natural sands with variable in situ densities were modeled. The results of the finite element analyses suggest that a direct correlation between qb0.1 and qc can be established at a given test site which is independent of footing width and depth and is relatively weakly dependent on the sands relative density if the zone of influence of the foundation considered is large enough.

The Simulation of the Southern Great Plains Nocturnal Boundary Layer and the Low-Level Jet with a High-Resolution Mesoscale Atmospheric Model

AbstractA field project over the Atmospheric Radiation Measurement–Cloud and Radiation Test Bed (ARM–CART) site during a period of several nights in September 2007 was conducted to explore the evolution of the low-level jet (LLJ). Data were collected from in situ (a multilevel tower) and remote (sodar) sensors, and the observed LLJ activity during the project was found to agree well with data from earlier studies regarding jet speed, height, and direction. To study nocturnal boundary layer (NBL) behavior, the Regional Atmospheric Modeling System was used to simulate the ARM–CART NBL field experiment and was validated against the data collected from the site. This model was run at high resolution for calculating the interactions among the various motions within the boundary layer and their influence on the surface. The model faithfully simulated the formation and dissolution of the low-level nocturnal jet during a synoptic situation in which low pressure with warm southerly advection replaced high pressure. An additional simulation at 32.5-m resolution was performed for the most stable 5.5-h period, using a turbulence scheme adjusted to allow for greater resolved turbulent kinetic energy, and the model reproduced the turbulence statistics as determined by a power spectrum. The benefit of the high-resolution simulation is evident in the much more realistically resolved model turbulent kinetic energy and the fluxes of momentum, heat, and water vapor.

Variability in surface BRDF at different spatial scales (30 m–500 m) over a mixed agricultural landscape as retrieved from airborne and satellite spectral measurements

Over the past decade, the role of multiangle remote sensing has been central to the development of algorithms for the retrieval of global land surface properties including models of the bidirectional reflectance distribution function (BRDF), albedo, land cover/dynamics, burned area extent, as well as other key surface biophysical quantities impacted by the anisotropic reflectance characteristics of vegetation. In this study, a new retrieval strategy for fine-to-moderate resolution multiangle observations was developed, based on the operational sequence used to retrieve the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5 reflectance and BRDF/albedo products. The algorithm makes use of a semiempirical kernel-driven bidirectional reflectance model to provide estimates of intrinsic albedo (i.e., directional-hemispherical reflectance and bihemispherical reflectance), model parameters describing the BRDF, and extensive quality assurance information. The new retrieval strategy was applied to NASA's Cloud Absorption Radiometer (CAR) data acquired during the 2007 Cloud and Land Surface Interaction Campaign (CLASIC) over the well-instrumented Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site in Oklahoma, USA. For the case analyzed, we obtained ~ 1.6 million individual surface bidirectional reflectance factor (BRF) retrievals, from nadir to 75° off-nadir, and at spatial resolutions ranging from 3 m to 500 m. This unique dataset was used to examine the interaction of the spatial and angular characteristics of a mixed agricultural landscape; and provided the basis for detailed assessments of: (1) the use of a land cover type-specific a priori knowledge in kernel-driven BRDF model inversions; (2) the interaction between surface reflectance anisotropy and instrument spatial resolution; and (3) the uncertainties that arise when sub-pixel differences in the BRDF are aggregated to a moderate resolution satellite pixel. Results offer empirical evidence concerning the influence of scale and spatial heterogeneity in kernel-driven BRDF models; providing potential new insights into the behavior and characteristics of different surface radiative properties related to land/use cover change and vegetation structure.

Components of an environmental observatory information system

Recently, an initiative within the hydrologic science and environmental engineering communities has emerged for the establishment of cooperative, large-scale environmental observatories. Scientists’ ability to access and use data collected within observatories to address broad research questions depends on the successful implementation of cyberinfrastructure. In this paper, we describe the architecture and functional requirements for an environmental observatory information system that supports collection, organization, storage, analysis, and publication of hydrologic observations. We then describe a unique system that has been developed to meet these requirements and that has been implemented within the Little Bear River, Utah environmental observatory test bed, as well as across a nation-wide network of 11 similar observatory test bed sites. The components demonstrated comprise an observatory information system that enables not only the management, analysis, and synthesis of environmental observations data for a single observatory, but also publication of the data on the Internet in simple to use formats that are easily accessible, discoverable by others, and interoperable with data from other observatories.

Evaluating the stochastic approach to shortwave radiative transfer in the tropical western Pacific

In the last decade numerous advances have been made in parameterizing cloud‐radiation interactions. One recent area of improvement involves statistical representations of the influence of three‐dimensional cloud fields on the domain averaged radiation. An off‐line comparison of a traditional plane‐parallel shortwave model against a stochastic model and observations is performed using four years of data from the Atmospheric Radiation Measurement Program's Tropical Western Pacific Clouds and Radiation Testbed site at Nauru Island. Cloud properties are derived from observed cloud chord lengths and input into the stochastic model, removing the necessity of explicitly simulating individual cloud fields and allowing for extended model runs. It is found that for certain cloud field geometries, as observed from the Nauru surface station, the stochastic radiative transfer model simulates more accurate surface fluxes than the traditional plane‐parallel model. Results suggest that the relationship between vertical extent of liquid cloud and liquid water path is one indicator of radiatively significant cloud field configurations as is the relationship between solar zenith angle and cloud fraction. The stochastic model performs best when the ratio between diffuse and total shortwave surface irradiance falls between 0.4 and 0.5. A simple parameterization based on criteria developed from these results is applied to the plane‐parallel modeled downwelling flux to represent the impact of complex cloud field geometry on the domain‐averaged radiation. The plane‐parallel simulations with the parameterization applied produce a mean downwelling flux that is 16 Wm−2 closer to observations than the plane‐parallel model results and 5 Wm−2 closer than the stochastic model results.

GOES sounding improvement and applications to severe storm nowcasting

An improved clear‐sky physical retrieval algorithm for atmospheric temperature and moisture is applied to the Geostationary Operational Environmental Satellite‐12 (GOES‐12) Sounder. A comparison with the microwave radiometer (MWR) measured total precipitable water (TPW) at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site from June 2003 to May 2005 shows that the TPW retrievals are improved by 0.4 mm over the legacy GOES Sounder TPW product. The Lifted Index (LI) derived product imagery (DPI) from the improved soundings better depicts the pre‐convective environment surrounding a tornadic supercell at Eagle Pass, Texas on 24 April 2007. Another severe storm case from 13 April 2006 demonstrates that the improved physical algorithm successfully detects low‐level moisture. Both cases show the new retrievals along with the derived products will help the forecasters with short‐term severe storm nowcasting.

Convective Planetary Boundary Layer Interactions with the Land Surface at Diurnal Time Scales: Diagnostics and Feedbacks

Abstract The convective planetary boundary layer (PBL) integrates surface fluxes and conditions over regional and diurnal scales. As a result, the structure and evolution of the PBL contains information directly related to land surface states. To examine the nature and magnitude of land–atmosphere coupling and the interactions and feedbacks controlling PBL development, the authors used a large sample of radiosonde observations collected at the southern Atmospheric Research Measurement Program–Great Plains Cloud and Radiation Testbed (ARM-CART) site in association with simulations of mixed-layer growth from a single-column PBL/land surface model. The model accurately predicts PBL evolution and realistically simulates thermodynamics associated with two key controls on PBL growth: atmospheric stability and soil moisture. The information content of these variables and their influence on PBL height and screen-level temperature can be characterized using statistical methods to describe PBL–land surface coupling over a wide range of conditions. Results also show that the first-order effects of land–atmosphere coupling are manifested in the control of soil moisture and stability on atmospheric demand for evapotranspiration and on the surface energy balance. Two principal land–atmosphere feedback regimes observed during soil moisture drydown periods are identified that complicate direct relationships between PBL and land surface properties, and, as a result, limit the accuracy of uncoupled land surface and traditional PBL growth models. In particular, treatments for entrainment and the role of the residual mixed layer are critical to quantifying diurnal land–atmosphere interactions.

Base load – displacement response of piles in sand

The paper presents the results of a series of laboratory and field model pile tests performed to study the factors controlling the base pressure – settlement reponse of piles in sand. One series of tests involved the installation and load testing of steel open- and closed-ended piles in loose sand contained in a large pile testing chamber. A second series involved tests on open- and closed-ended steel piles and a concrete bored pile at a dense sand test bed site. The experiments were designed to investigate the effects of pile type, sand consistency, and installation resistance on a pile’s base response during static loading. The tests revealed that both the base capacity and stiffness of piles in sand are controlled by the degree of prestress imposed on the soil below the pile tip. Simple expressions, which require the small strain stiffness and cone penetration test data as the input parameters, are developed to predict the base pressure – settlement response. The final part of the paper employs other field tests on full-scale displacement piles and bored piles to verify the validity of the proposed approach.

Effect of Friction Fatigue on Pile Capacity in Dense Sand

The paper presents the results of a series of field tests performed to study the causes of friction fatigue experienced by displacement piles. Four instrumented model piles were installed at a dense sand test-bed site. The test series was designed to impose different levels of cyclic loading during pile installation. Static and cyclic load tests were subsequently performed to study the differences in the axial capacities developed for ostensibly monotonic and cyclic installations. The test results indicated that the mobilized horizontal effective stress regime that controls pile side friction primarily depends on the in situ sand state, as reflected by the cone penetration test (CPT) qc resistance. A zone of highly stressed sand that produced a concentration of high shear resistance was mobilized in the vicinity of the pile base. The horizontal effective stress that acted on the pile shaft reduced in response to cyclic loading, with the largest reductions occurring for high-intensity cyclic loading or when the pile had experienced only a few load cycles during installation. Although cyclic loading caused a reduction in the horizontal effective stress that acted on the pile shaft, the elevated stress built up in the vicinity of the pile base during installation remained higher than that remote from the base. The elevated stress in the vicinity of the pile base only dissipated after cyclic tension loading had been applied.

Rainfall Profiling Using Atmospheric Radiation Measurement Program Vertically Pointing 8-mm Wavelength Radars

Abstract An attenuation-based method to retrieve vertical profiles of rainfall rate from vertically pointing Ka-band radar measurements has been refined and adjusted for use with the U.S. Department of Energy’s cloud radars deployed at multiple Atmospheric Radiation Program (ARM) test bed sites. This method takes advantage of the linear relationship between the rainfall rate and the attenuation coefficient, and can account for a priori information about the vertical profile of nonattenuated reflectivity. The retrieval method is applied to a wide variety of rainfall events observed at different ARM sites ranging from stratiform events with low-to-moderate rainfall rates (∼5 mm h−1) to heavy convective rains with rainfall rates approaching 100 mm h−1. The Ka-band attenuation-based retrieval results expressed in both instantaneous rainfall rates and in rainfall accumulations are compared to available surface data and measurements of a scanning C-band precipitation polarimetric radar located near the Darwin, Australia, ARM test bed site. The Ka-band retrievals are found to be in good agreement with the C-band radar estimates, which are based both on conventional radar reflectivity approaches and on polarimetric differential phase shift measurements. Typically, the C-band–Ka-band radar estimate differences are within the expected retrieval uncertainties. The magnitude of the Ka-band rainfall-rate estimate error depends on the retrieval resolution, rain intensity, and uncertainties in the profiles of nonattenuated reflectivity. It is shown that reasonable retrieval accuracies (∼15%–40%) can be achieved for a large dynamic range of observed rainfall rates (4–100 mm h−1) and the effective vertical resolution of about 1 km. The potential enhancements of the Ka-band attenuation-based method by including a priori information on vertical profiles of nonattenuated reflectivity and increasing the height range of the retrievals by using Ka-band polarization measurements are also discussed. The addition of the precipitation products to the suite of ARM hydrometeor retrievals can enhance the overall characterization of the vertical atmospheric column.

A Comparison of GOES Sounder– and Cloud Lidar- and Radar-Retrieved Cloud-Top Heights

Abstract An assessment of the performance of the Geostationary Operational Environmental Satellite (GOES) sounder cloud-top pressure product is presented. GOES sounder cloud-top-height data were compared with values derived from a consensus cloud boundary dataset that utilizes data from a cloud lidar and a cloud radar located at the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program’s Cloud and Radiation Test Bed (CART) site in Lamont, Oklahoma. Comparisons were performed from April 2000 to March 2002. A temporal filtering process was applied to the cloud lidar and cloud radar output so that a representative picture of the cloud field on the same spatial scale of the GOES sounder could be derived. Comparisons between the GOES sounder and ground-based cloud boundary measurements yielded a mean difference of 1772 m and a standard deviation of 1733 m. The difference between GOES cloud-top-height and ground-based retrievals is within ±500 m for 22% of the retrievals and within ±1500 m for 56% of the retrievals. These results are comparable to findings in similar studies that utilized the MODIS Airborne Simulator.

Measurement of Low Amounts of Precipitable Water Vapor Using Ground-Based Millimeterwave Radiometry

Abstract Extremely dry conditions characterized by amounts of precipitable water vapor (PWV) as low as 1–2 mm commonly occur in high-latitude regions during the winter months. While such dry atmospheres carry only a few percent of the latent heat energy compared to tropical atmospheres, the effects of low vapor amounts on the polar radiation budget—both directly through modulation of longwave radiation and indirectly through the formation of clouds—are considerable. Accurate measurements of PWV during such dry conditions are needed to improve polar radiation models for use in understanding and predicting change in the climatically sensitive polar regions. To this end, the strong water-vapor absorption line at 183.310 GHz provides a unique means of measuring low amounts of PWV. Weighting function analysis, forward model calculations based upon a 7-yr radiosonde dataset, and retrieval simulations consistently predict that radiometric measurements made using several millimeter-wavelength (MMW) channels near the 183-GHz line, together with established microwave (MW) measurements near the 22.235-GHz water-vapor line and ∼31-GHz atmospheric absorption window can be used to determine within 5% uncertainty the full range of PWV expected in the Arctic. This combined capability stands in spite of accuracy limitations stemming from uncertainties due to the sensitivity of the vertical distribution of temperature and water vapor at MMW channels. In this study the potential of MMW radiometry using the 183-GHz line for measuring low amounts of PWV is demonstrated both theoretically and experimentally. The study uses data obtained during March 1999 as part of an experiment conducted at the Department of Energy’s Cloud and Radiation Testbed (CART) site near Barrow, Alaska. Several radiometers from both NOAA and NASA were deployed during the experiment to provide the first combined MMW and MW ground-based dataset during dry Arctic conditions. Single-channel retrievals of PWV were performed using the MW and MMW data. Discrepancies in the retrieved values were found to be consistent with differences observed between measured brightness temperatures (TBs) and forward-modeled TBs based on concurrent radiosonde profiles. These discrepancies are greater than can be explained by radiometer measurement error alone; errors in the absorption models and uncertainty in the radiosonde measurements contribute to the discrepancies observed. The measurements, retrieval technique, and line model discrepancies are discussed, along with difficulties and potential of MMW/MW PWV measurement.

Cloud cover comparisons of the MODIS daytime cloud mask with surface instruments at the north slope of Alaska ARM site

This paper compares daytime cloud fraction derived from the Moderate Resolution Imaging Spectrometer (MODIS), an imager on the National Aeronautics and Space Administration's Earth Observing System Aqua and Terra platforms, to observations from a suite of surface-based instrumentation located at the Department of Energy's atmospheric radiation measurement (ARM) program North Slope of Alaska (NSA) Clouds and Radiation Testbed site. In this systematic comparison of satellite-to-surface measurements, 3650 cases are analyzed from February through September 2001. The surface instruments used in these comparisons include the Vaisala Ceilometer (VCEIL), the Micropulse Lidar (MPL), the Active Remote Sensing of Clouds (ARSCL) composite laser-derived data product, the Whole-Sky Imager (WSI), and the Normal Incidence Pyrheliometer (NIP). In terms of the active sensors, VCEIL cloud cover results compare to within /spl plusmn/20% of MODIS results 77% of the time. As expected, VCEIL is found to be insensitive to optically thin high-level clouds. MPL results are consistent with MODIS in 83% of the cases; however, the MPL preliminary.cbh variable reports spurious clouds in clear-sky conditions. The ARSCL composite laser-derived data product agrees with MODIS in 81% of the cases, improving upon high cloud detection of the VCEIL, while eliminating the spurious clear-sky cloud detections in the MPL preliminary.cbh variable. For the passive WSI, cloud cover agrees with the MODIS cloud fraction in 74% of the cases, with the difference primarily caused by the insensitivity of the WSI to thin clouds. Detailed analysis of individual cases shows that the MODIS cloud mask generally detects more thin cirrus than the surface-based instruments, but it sometimes fails to detect low-level cumulus and fog over the ARM NSA site.

In situ aerosol profiles over the Southern Great Plains cloud and radiation test bed site: 2. Effects of mixing height on aerosol properties

The goal of this study was to determine under what meteorological conditions, if any, measurements of aerosol properties made at the Earth's surface are representative of aerosol properties measured within the column of air above the surface. Specifically, this study uses instrumentation from the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains (SGP) site to determine how the observed mixing height (MH) and the degree of mixing affects the vertical variation of aerosol extensive and intensive properties. The MH was estimated by applying the Heffter [1980] technique with a critical lapse rate of 0.001 K m−1 to the available radiosonde data. This estimate was then used to determine whether each vertical aerosol profile flight leg from 59 flights was within or above the atmospheric boundary layer (ABL). Although the aerosol extensive properties, such as light absorption by particles σap, light scattering by particles σsp, and total extinction by particles σext measured within the ABL were highly correlated with the surface measurements (R2 = 0.74, 0.88, and 0.88, respectively), the airborne measurements of σap were systematically lower (slope = 0.77). By contrast, the σsp and σext regression line slopes were 0.99 and 1.00. The aerosol extensive properties measured above the ABL were poorly correlated with surface values and were almost an order of magnitude lower than the simultaneous measurements made within the ABL. Aerosol intensive properties such as the single‐scattering albedo ϖo, the hemispheric backscatter fraction b, and the Ångström exponent å exhibited a similar behavior (R2 = 0.74, 0.61, and 0.55, respectively) but had regression line slopes within the ABL of 0.88, 0.75, and 0.62, respectively. There were no statistically significant correlations between the intensive aerosol properties measured above the ABL and those measured at the surface. Limiting the analysis to well‐mixed days with near‐neutral static stability did not significantly improve the results. Thus the hypothesis that the best agreement between surface measurements and those within the ABL will occur when the atmosphere is well mixed was not supported by this data set.

In situ aerosol profiles over the Southern Great Plains cloud and radiation test bed site: 1. Aerosol optical properties

Aerosol optical properties were measured over the Southern Great Plains (SGP) cloud and radiation test bed site using a light aircraft (Cessna C‐172N). The aircraft flew level legs at altitudes between 500 m and 3500 m several times per week over the course of 2 years in order to obtain a statistically representative data set of in situ aerosol vertical profiles. Instrumentation on the aircraft was similar to that at the surface SGP site so that measurements at the surface and aloft could easily be compared. Measured parameters included total light scattering, backscattering, and absorption, while calculated parameters included single‐scattering albedo, backscatter fraction, and Ångström exponent. Statistical plots of aerosol optical properties and their variation in the lower column (0–4000 m) showed that over the course of the 2 years studied, albedo, backscatter fraction, and Ångström exponent were fairly invariant with altitude (at least up to 1800 m). Despite the vertical consistency the correlation between column average and surface values for single‐scattering albedo, backscatter fraction, and Ångström exponent tended to be quite low, with R2 ranging from 0.3 to 0.6 and linear regression slopes ranging from 0.2 to 0.6. These results suggest that long‐term surface aerosol measurements capture the column aerosol properties but may not be as representative of day‐to‐day variations in the column. Comparison of aerosol optical depth (AOD) calculated from the vertical profiles with other measurements of AOD made at SGP (i.e., by the Cimel Sun photometer and the multifilter rotating shadowband radiometer (MFRSR)) showed fair correlation (R2 ∼ 0.7 Cimel, R2 ∼ 0.8 MFRSR), although the aircraft AODs tend to have a consistent offset of −0.04, even after incorporating a correction for supermicrometer aerosol and stratospheric aerosol.

Nighttime Multilayered Cloud Detection Using MODIS and ARM Data

This study reports on recent progress toward the discrimination between pixels containing multilayered clouds, specifically optically thin cirrus overlying lower-level water clouds, and those containing single-layered clouds in nighttime Moderate Resolution Imaging Spectroradiometer (MODIS) data. Cloud heights are determined from analysis of the 15-m mC O 2 band data (i.e., the CO 2-slicing method). Cloud phase is inferred from the MODIS operational bispectral technique using the 8.5- and 11-mm IR bands. Clear-sky pixels are identified from application of the MODIS operational cloud-clearing algorithm. The primary assumption invoked is that over a relatively small spatial area, it is likely that two cloud layers exist with some areas that overlap in height. The multilayered cloud pixels are identified through a process of elimination, where pixels from single-layered upper and lower cloud layers are eliminated from the data samples. For two case studies (22 April 2001 and 28 March 2001), ground-based lidar and radar observations are provided by the Atmospheric Radiation Measurement (ARM) Program’s Southern Great Plains (SGP) Clouds and Radiation Test Bed (CART) site in Oklahoma. The surface-based cloud observations provide independent information regarding the cloud layering and cloud height statistics in the time period surrounding the MODIS overpass.