With a global frequency of occurrence near 30%, cirrus clouds wield a strong influence over the radiation budget of the Earth’s climate system due to their location in the upper troposphere. Currently, global climate models (GCMs) are unable to accurately represent cirrus cloud feedbacks on the radiation and hydrological cycles due to a lack of understanding of how to parameterize the effects of cirrus. This inability to parameterize the microphysical properties of cirrus clouds can be attributed to a general lack of observations of these clouds and their dynamical environment in the upper troposphere. While aircraft provide direct measurements in this region, their use is limited due to expense, and ground-based remote sensors such as radars and lidars, while also quite useful, are limited to just a few locales. Satellite measurements, on the other hand, are global in nature but limited in the sense that the cloud properties must be derived through the use of complicated inversion algorithms. One of the newer satellite instruments currently on board the NASA Earth Observing System Terra and Aqua platforms, is the moderate resolution Imaging Spectroradiometer. MODIS observes upwelling reflectance and radiance from the Earth's atmosphere and surface in 36 narrow spectral intervals ranging from .62 μm to 14.385 μm. By combining measurement channels that are non absorbing and thus sensitive to total cross sectional area with other channels that are absorbing and include sensitivities to particle size, the observed radiances can provide estimates of optical depth (τ) and effective radius (r_e). Ice water path is calculated directly from these values. Validation of the retrievals is essential for eventual development of parameterizations that can be assimilated into GCMs.

A method is developed to retrieve total Cloud Optical Depth (COD) from broadband Global Solar Radiation detected by paronometer, and available approaches to input aerosol/molecular/gas parameters for the COD retrieval are presented. Aerosol Optical Depth (AOD) retrieved from pyrheliometer data and simultaneous visibility measurement in the clear days are used in building an empirical relationship between AOD and visibility. The relationship is used in determining AOD in the cloudy days. By using the method, the retrieved CODs over 11 meteorological observatories in China during 2001 are compared with MODIS COD products. The difference between the yearly-mean CODs from hourly-accumulated paronometer data and the MODIS COD is less than 34.5% for every site. The agreement between yearly-mean COD from daily GSR data and MODIS COD is also good for all 11 sites except for Geermu site locating over Qinghai-Tibet Plateau. Furthermore, CODs over Beijing and Zhengzhou during 1961-2001 are analyzed.

This paper conducts a preliminary assessment of the cloud detection capability of the Japanese Global Imager (GLI). Cloud detection results from the satellite borne instrument are compared to other satellite, aircraft and ground-based observations. The performance is similar to that of the MODIS results.

Many satellite-derived products such as the atmospheric wind vector depend their accuracy on the accuracy of the estimated cloud top altitude. The uncertainty in the derived cloud top altitude occurs mainly when there is thin semitransparent cloud where the cloud radiation is contaminated by radiation from the surface and low cloud. Further, validation of the derived cloud top altitude is not easy task, simply due to lack of truth data. Here, we use ground based rawinsonde, radar, and lidar data for the validation of the cloud top altitude derived from GOES-9 satellite data. The preliminary results show that the infrared-water vapor method compares better than the single infrared method for all of the ground truth data.

Operational Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of cloud optical thickness and effective particle radius employ well-known solar reflectance techniques using pre-calculated reflectance look-up tables. We develop a methodology for evaluating the quantitative uncertainty in simultaneous retrievals of cloud optical thickness and particle size for this type of algorithm and present example results. The technique uses retrieval sensitivity calculations derived from the reflectance look-up tables, coupled with estimates for the effect of various error terms on the uncertainty in inferring the reflectance at cloud-top. The error terms include the effects of the measurements, surface spectral albedos, and atmospheric corrections on both water and ice cloud retrievals. Results will deal exclusively with pixel-level uncertainties associated with plane-parallel clouds; real-world radiative departures from a plane-parallel model are an additional consideration. While we demonstrate the uncertainty technique with operational 1 km MODIS retrievals from the NASA Earth Observing System (EOS) Terra and Aqua satellite platforms, the technique is generally applicable to any reflectance-based satellite- or air-borne sensor retrieval using similar spectral channels.

A small portable lidar system was recently used to derive aerosol optical concentrations from ground and aircraft platforms. The mini lidar uses a telescope setup with a relatively wide field of view allowing for measurements from close in (~60 m range) with no near field correction. In order to account for the large dynamic range, a custom logarithmic amplifier is used. Lidar measurements have been made in Hawaii and examples will be shown. More recently the Lidar was mounted on an aircraft for an experiment in the United Arab Emirates. In this case, the Lidar system was used to looking up, forward and down. The Lidar measurements looking up and down provided vertical profiles of aerosol concentrations. The lidar looking forward were used to derive quantitative aerosol extinction values using an existing and a new approach. Preliminary examples of this UAE data are shown. Being able to model aerosol phase functions is important for both satellite and Lidar aerosol retrievals. Mie theory is adequate for spherical particles but complex aerosols such as dust and organics are more difficult to model. Here we discuss phase function measurements we have made with our ground based polar nephelometer for sea salt and more recently for dust in the United Arab Emirates.

Silicate dusts, volcanic ash clouds and Asian dust, are well detected by the 'split-window' method, which calculates the brightness temperature difference of the 11 and 12 μm bands. Volcanic plumes containing less ash are enhanced by the difference of the visible and near infrared bands of NOAA/AVHRR data. In order to supplement these difference images and improve the discrimination of volcanic ash- rich/poor plumes and of Asian dust from various meteorological clouds, various combinations of AVHRR imagery were investigated. It was found that the differences of the 3.7 and 11 μm bands and of the 1.6 μm and visible bands are useful to distinguish between thick clouds and dusts. Colour composite images containing the 1.6 or 3.7 μm bands are useful for distinguishing the objects from any meteorological clouds, because these bands are sensitive to droplet size.

A number of factors affect the accuracy of aerosol retrievals from satellite imaging radiometers, including algorithm assumptions, the quality of the associated cloud masks, the prescribed aerosol optical and microphysical models, and calibration uncertainties. In this paper, we highlight a concerted effort by the Terra Multi-angle Imaging SpectroRadiometer (MISR) team to evaluate the accuracy and stability of the instrument's radiometric calibration, with the twofold objective of (1) making improvements in the absolute and relative calibration where supported by multiple lines of evidence, and (2) evaluating the effect of those calibration refinements on aerosol retrievals. Aspects of the instrument's on-board calibrator design, including careful pre-flight handling of the Spectralon diffusers and the novel use of detector-based standards, have contributed to excellent long-term radiometric stability. In addition, multiple methodologies, including comparisons with other Terra sensors, in-flight and laboratory tests involving AirMISR (the airborne counterpart to MISR), lunar observations, camera-to-camera radiometric comparisons at specialized viewing geometries, and investigations using surface-based radiometer data over dark water sites have provided a detailed picture of radiometric performance at the low light levels typical of a large fraction of global aerosol observations. We examine the sensitivity of aerosol property retrievals to small band-to-band and camera-to-camera calibration adjustments, and demonstrate the importance of calibration in meeting climate-quality accuracy requirements. Because combining downward-looking (satellite-based) and upward-looking (surface-based) radiometers can constrain the optical properties of an aerosol column to a greater extent than possible from either vantage point by itself, achieving radiometric consistency, or “closure” between them is essential to establishing a long-term aerosol/climate observing system.

The optical parameters of the Asian dust over the desert in China and the surface reflectance were estimated simultaneously, using reflectances and polarizations at the wavelength 670 nm in several points selected from ADEOS/POLDER data taken on April 10, 1997. It was assumed that the land surface is the diffuse reflector and the number size distribution of the Asian dust is represented by the Junge power-law. The optical parameters of the dust layer, such as the optical thickness, refractive index of the dust aerosol and index of the Junge power-law, and the ground reflectance were determined such that the sum of the relative absolute error between the observed reflectance and polarization and those obtained from the simulation of radiative transfer in the atmosphere-ground system is minimum. As a result, it was found that the refractive index of Asian dust is 1.4 to 1.5, the optical thickness of dust layer is 0.1 to 0.2, the index of Junge power-law is -5.3 to -6.0 and the surface reflectance is 0.3 at the wavelength 670 nm.

MODIS aerosol retrievals over ocean from Terra and Aqua platforms are available from the Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) datasets generated at NASA Langley Research Center (LaRC). Two aerosol products are reported side by side. The primary M product is generated by subsetting and remapping the multi-spectral (0.44 - 2.1 μm) MOD04 aerosols onto CERES footprints. MOD04 processing uses cloud screening and aerosol algorithms developed by the MODIS science team. The secondary (AVHRR-like) A product is generated in only two MODIS bands: 1 and 6 on Terra, and ` and 7 on Aqua. The A processing uses NASA/LaRC cloud-screening and NOAA/NESDIS single channel aerosol algorthm. The M and A products have been documented elsewhere and preliminarily compared using two weeks of global Terra CERES SSF (Edition 1A) data in December 2000 and June 2001. In this study, the M and A aerosol optical depths (AOD) in MODIS band 1 and (0.64 μm), τ_1M and τ_1A, are further checked for cross-platform consistency using 9 days of global Terra CERES SSF (Edition 2A) and Aqua CERES SSF (Edition 1A) data from 13 - 21 October 2002.

The knowledge of the global distribution of tropospheric aerosols is important for studying effects of natural aerosols on global climate. Chemical transport models relying on assimilated meteorological fields and accounting for aerosol advection by winds and removal processes can simulate such distribution of atmospheric aerosols. However, the accuracy of global aerosol modeling is yet limited. The uncertainty in location and strength of the aerosol emission sources is a major factor limiting accuracy of global aerosol transport modeling. This paper describes an effort to retrieve global sources of fine mode aerosol from global satellite observations by inverting GOCART aerosol transport model. The method uses an adjoint operation to the aerosol transport model that allows performing inversion with original space (2 x 2.5 degrees) and time (20-60 minutes) resolution of GOCART model. The approach is illustrated by numerical tests and applied to the retrieval global aerosol sources (location and strength) from a combination of MODIS and AERONET observations.

The surface reflectance ratios for certain land classes in Japan between the visible and infrared bands were computed using the observed sky radiometer data and several data sets of Terra/MODIS in 2002 and 2003. They were found to be different from those in USA. The values of aerosol optical thickness τ_a were retrieved from Terra/ASTER and Landsat-7/ETM+ data sets over Japan assuming new surface reflectance ratios. We found a good agreement between the retrieved and observed aerosol optical thickness values at our study site. This study suggested the necessity of further works on local and seasonal variations in surface reflectance ratios.

Retrieval of vertically integrated water vapor amount (precipitable water) is proposed using near infrared channels of Global Imager onboard Advanced Earth Observing Satellite-II (GLI/ADEOS-II). The principle of retrieval algorithm is based upon that adopted with Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Earth Observing System (EOS) satellite series. Simulations were carried out with GLI Signal Simulator (GSS) to calculate the radiance ratio between water vapor absorbing bands and non-absorbing bands. As a result, it is found that for the case of high spectral reflectance background (a bright target) such as the land surface, the calibration curves are sensitive to the precipitable water variation. It turns out that aerosol loading has little influence on the retrieval over a bright target for the aerosol optical thickness less than about 1.0 at 500 nm wavelength. A preliminary analysis of GLI data was also carried out and the retrieved result is discussed. It is also anticipated that simultaneous retrieval of the water vapor amount using GLI data along with other channels will lead to improved accuracy of the determination of surface geophysical properties, such as vegetation, ocean color, and snow and ice, through the better atmospheric correction.

The Ozone Monitoring Instrument (OMI), a nadir-viewing near-UV/Visible CCD spectrometer, was launched on NASA's EOS-Aura satellite platform on 15 July 2004 into a sun-synchronous, polar orbit with an equator crossing time of 13:45h (ascending node). OMI measurements cover the spectral region of 270-500 nm with a spectral resolution between 0.42 nm and 0.63 nm and a nominal ground footprint of 13x24 km² at nadir. Global coverage is achieved in one day. The very high spatial resolution of OMI measurements set a new standard for trace gas and air quality monitoring from space. Combined with daily global coverage, this significantly advances our ability to answer outstanding questions on air chemistry, including the determination of BrO sources in mid and low latitudes, BrO-O₃ anti-correlations as a function of latitude, and the production of formaldehyde in cities of the developing world. We give an overview of the OMI instrument and introduce the operational trace gas retrieval scheme for BrO, HCHO, and OClO that is based on a direct, non-linear fitting approach of observed radiances, including corrections for spectral undersampling. We present first results for tropospheric BrO and HCHO, an important element in air quality monitoring. Only limited results are currently available for OClO, an element in the destruction cycle of polar stratospheric ozone, due to the lack of OMI observations at a time of the year where OClO loading is significantly above the detection limit from space.

Carbon monoxide (CO) is an important tropospheric trace species and can serve as a useful tracer of atmospheric transport. The Measurements of Pollution In The Troposphere (MOPITT) instrument uses the 4.7 μm CO band to measure the spatial and temporal variation of the CO profile and total column amount in the troposphere from space. Launched in 1999 on board the NASA Terra satellite, the MOPITT views the earth with a pixel size 22 km by 22 km and a cross-track swath that measures a near-global distribution of CO every 3 days. In the operational MOPITT CO retrieval algorithm (V3; Version 3), surface skin temperature (Ts) and emissivity (E) are retrieved simultaneously with the CO profile. The accuracy of E and Ts is crucial for obtaining the CO retrieval within the 10% accuracy from the MOPITT measurements. However, because both Ts and E are retrieved from the same piece of information from the MOPITT measurements, the accuracy of both valuables may be limited. Extra surface skin temperature information is needed to determine surface emissivity, and vice versa. In this study, we use MODIS Ts within the MOPITT FOVs, in conjunction with those MOPITT signals most sensitive to the background scene, to compute the surface emissivity through an iterative retrieval algorithm. A monthly 1degree grid averaged 4.7 μm surface emissivity map is generated. The evaluation of the accuracy of this monthly 1 degree grid averaged 4.7 μm surface emissivity map is presented and its impacts on the retrievals of tropospheric CO profiles from the MOPITT measurements are also discussed.

The experimental data on CO₂ and O₂ detection in atmosphere using Fabry-Perot technique are presented. The atmosphere's irradiance measurements are an important tool for the remote sensing study. We show results from lab, ground and flight testing of a new instrument called FPICC (Fabry-Perot Interferometer for Column CO₂) which is intended for a very precise measurements of atmospheric carbon dioxide and oxygen. The optical setup consists of three channels. The first channel is built to measure the carbon dioxide. This channel operates using the reflected sunlight off the ground and solid Fabry-Perot etalon to restrict the measurement to light in CO₂ absorption bands. The free spectral range of the etalon is calculated to be equal to the almost regular spacing between the CO₂ spectral bands located near 1,571 μm, R band, where CO₂ absorption is significant. The precise alignment of the transmission peaks of the Fabry-Perot etalon to the CO₂ absorption lines is achieved through altering the refractive index of the material (fused silica) using its temperature dependence. The second and third channels foucs on the O₂ A band (759 - 771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and two different pre-filters. The first pre-filter selects a spectral range around 762 nm which is between the P and R branches, where the absorption coefficient is insensitive to temperature, but is sensitive to pressure changes and therefore to the variations in the O₂ column. The second pre-filter is selecting several absorption bands between 765 and 770 nm, which are more sensitive to temperature changes. The experimental data presented show excellent agreement with our theoretical expectations. They are recorded at different gas pressures, temperatures and different weather conditions. Some of the major advantages of the optical setup are its compactness, high sensitivity, high signal-to-noise ratio, and stability.

The tri-agency Integrated Program Office (IPO) manages the development of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). NPOESS will replace the Defense Meteorological Satellite Program (DMSP) and Polar-orbiting Operational Environmental Satellites (POES) that have provided global data for weather forecasting and environmental monitoring for over 40 years. Beginning in late 2009, NPOESS spacecraft will be launched into three orbital planes to provide significantly improved operational capabilities and benefits to satisfy critical civil and national security requirements for space-based, remotely sensed environmental data. NPOESS will observe more phenomena simultaneously from space than its operational predecessors and deliver a data volume significantly greater than the POES and DMSP systems with substantially improved delivery of data to users. Higher (spatial, temporal, and spectral) resolution and more accurate imaging and sounding data will enable improvements in short- to medium-range weather forecasts. NPOESS will support the operational needs of meteorological, oceanographic, environmental, climatic, and space environmental remote-sensing programs and provide continuity of data for climate researchers. With the development of NPOESS, we are evolving operational “weather” satellites into integrated global environmental observing systems by expanding our capabilities to observe, assess, and predict the total Earth system - atmosphere, ocean, land, and the space environment.

The Atmospheric Infrared Sounder (AIRS) was launched in May 2002. Along with two companion microwave sensors, it forms the AIRS Sounding Suite. This system is the most advanced atmospheric sounding system to date, with measurement accuracies far surpassing those available on current weather satellites. The data products are calibrated radiances from all three sensors and a number of derived geophysical parameters, including vertical temperature and humidity profiles, surface temperature, cloud fraction, cloud top pressure, and ozone burden. These products are generated under cloudy as well as clear conditions. An ongoing calibration/validation effort has confirmed that the system is very accurate and stable, and most of the geophysical parameters have been validated. AIRS is in some cases more accurate than any other source and can therefore be difficult to validate, but this offers interesting new research opportunities. The applications for the AIRS products range from numerical weather prediction to atmospheric research - where the AIRS water vapor products near the surface and in the mid to upper troposphere will make it possible to characterize and model phenomena that are key for short-term atmospheric processes, such as weather patterns, to long-term processes, such as interannual cycles (e.g., El Niño) and climate change.

The Ozone Mapping and Profiler Suite (OMPS) will collect total column and vertical profile ozone data and continue the daily global data produced by the current operational satellite monitoring systems, the Solar Backscatter Ultraviolet radiometer (SBUV/2) and the Total Ozone Mapping Spectrometer (TOMS), but with higher fidelity. The collection of this data will contribute to fulfilling US treaty obligations to monitor ozone depletion for the Montreal Protocol. OMPS has been selected to fly on the National Polar-Orbiting Operational Satellite System (NPOESS) spacecraft - the next generation of polar orbiting environmental satellites. The first OMPS flight unit will fly on the NPOESS Preparatory Project (NPP) spacecraft. On-orbit calibration of the OMPS instruments is critical to maintaining quality data products. A number of signal corrections and calibrations are applied on-board the sensor and in ground processing to account for instrument non-idealities and to convert measured digital signals to calibrated radiances and irradiances. Three fundamental on-orbit calibration measurements are made to provide the required data to perform the radiometric calibration and trending.

This article proposes a series of strategies for improving the computer process of the Synthetic Aperture Radar (SAR) signal treatment, following the three usual lines of action to speed up the execution of any computer program. On the one hand, it is studied the optimization of both, the data structures and the application architecture used on it. On the other hand it is considered a hardware improvement. For the former, they are studied both, the usually employed SAR process data structures, proposing the use of parallel ones and the way the parallelization of the algorithms employed on the process is implemented. Besides, the parallel application architecture classifies processes between fine/coarse grain. These are assigned to individual processors or separated in a division among processors, all of them in their corresponding architectures. For the latter, it is studied the hardware employed on the computer parallel process used in the SAR handling. The improvement here refers to several kinds of platforms in which the SAR process is implemented, shared memory multicomputers, and distributed memory multiprocessors. A comparison between them gives us some guidelines to follow in order to get a maximum throughput with a minimum latency and a maximum effectiveness with a minimum cost, all together with a limited complexness. It is concluded and described, that the approach consisting of the processing of the algorithms in a GNU/Linux environment, together with a Beowulf cluster platform offers, under certain conditions, the best compromise between performance and cost, and promises the major development in the future for the Synthetic Aperture Radar computer power thirsty applications in the next years.

Greenhouse gases Observing SATellite (GOSAT) is a Japanese satellite to monitor column density of greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄) globally from space. GOSAT will be launched in 2008. The data measured by a GOSAT sensor and ground-based monitoring station data will be used into an atmospheric transport inverse model to identify source/sink amount of CO₂ in a sub-continental scale. One of the main GOSAT sensors is a nadir-looking Fourier Transform Spectrometer (FTS), which covers Short Wavelength Infrared (SWIR) region to measure column density of CO₂. National Institute for Environmental Studies (NIES) is promoting researches on CO₂ and CH₄ sensitivity analysis, error analysis, data retrieval algorithm study, ground-based/air-borne validation strategy, and a plan of inverse model study for the SWIR FTS. A Bread-board model (BBM) of the SWIR FTS was built and tested by ground-based and airborne measurements. Several sets of the CO₂ and CH₄ radiance spectra over rice fields were obtained by the test measurements, and it was confirmed that the airborne measurements with a vibration insulator are effective for onboard measurements. Moreover, several improvement items of BBM have become clear.

A computer model of the MODIS attenuated (with screen down) solar calibration has been developed. Observed (visible) focal plane variations are presented and compared with modeled results. The agreement is quite good over the full range of scan mirror and solar motions. Causes for discrepancies are discussed.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of five scientific instruments onboard the NASA EOS Terra spacecraft, launched December 1999. Early on-orbit calibration and characterization of Terra MODIS showed noticeable mirror side dependent degradation, particularly in the visible spectral region through the use of its on-board calibrators (OBC). These calibrators, including a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system and a spectro-radiometric calibration assembly (SRCA), are operated at either weekly or monthly frequency, tracking the sensor’s calibration stability and updating calibration coefficients. This paper describes an approach developed shortly after Terra’s launch which studies MODIS reflective solar bands (RSB) mirror side dependent degradation and presents its on-orbit time series trending results. The approach uses simultaneous Earth scene observations from MODIS and the Multi-angle Imaging Spectroradiometer (MISR) on the Terra spacecraft. To reduce the effects due to Earth scene variations, only MODIS/MISR radiance or response ratios averaged over many spatially and spectrally matched pixels are used in the analysis and support for the calibration. Our results show that over a five-year period MODIS detector response ratios of mirror side 2 relative to mirror side 1 degraded 7.0%, 5.0% and 2.5% in bands 8 (0.41μm), 9 (0.44μm) and 3 (0.47μm) at the nadir view. The change in the mirror side ratio is much smaller for bands at longer wavelengths. The results also show that the change in the mirror side ratio is strongly dependent on the viewing angle. The impact of the degradation and response versus scan angle corrections to the RSB calibration is discussed.

Response versus scan angle (RVS) is a key calibration parameter for remote sensing radiometers that make observations using a scanning optical system, such as a doubled sided scan mirror (MODIS and GLI) or a rotating telescope (SeaWiFS and VIIRS). This is because the calibration is typically performed at a fixed viewing angle whereas the Earth scene observations are made over a range of viewing angles and the system’s response is a function of the scan angle. The NASA EOS Terra MODIS has been in operation for more than four years since its launch in December 1999. It has 36 spectral bands covering wavelengths from visible (VIS) to long-wave infrared (LWIR). It is a cross-track scanning radiometer with a two-sided paddle wheel scan mirror, making observations over a wide field of view (FOV) of ±55° from nadir thereby enabling frequent global coverage. Due to pre-launch measurement limitations, the Terra MODIS thermal emissive bands (TEB) RVS characterization did not produce valid data sets that could be used to derive a reliable system level RVS. Because of this, a RVS was developed for use at launch and subsequent efforts have been made to characterize the RVS using on-orbit observations. This paper describes the Terra MODIS on-orbit characterization of TEB RVS, including the data from scanning the instrument’s closed nadir aperture door (CNAD) and the use of Earth view data collected during spacecraft deep space maneuvers (DSM). Comparisons of pre-launch analysis and early on-orbit measurements are also provided. Noticeable improvements have been made for several thermal emissive bands for observations at large angles of incidence (AOI). Using the correct RVS improves the image quality and the radiometric calibration accuracy. For bands 34-36, an adjustment of as much as 0.5-1.5K can be made at the end of scan (worst case) for mirror side 2. The impacts at smaller AOI and from mirror side 1 are much smaller. Based on RVS comparison studies and science test results, the on-orbit derived DSM RVS has been chosen for the ongoing L1B data processing and future reprocessing.

Significant improvements have been made to the MODIS cloud mask (MOD35) in preparation for Collection 5 reprocessing and forward stream data production. Most of the modifications are realized for nighttime scenes where polar and oceanic regions will see marked improvement. For polar night scenes, two new spectral tests using the 7.2 μm water vapor absorption band have been added as well as updates to the 3.9-12 μm and 11-12 μm cloud tests. More non-MODIS ancillary data has been added for nighttime processing. Land and sea surface temperature maps provide crucial information for middle and low-level cloud detection and lessen dependence on ocean variability tests. Sun-glint areas are also improved by use of sea surface temperatures to aid in resolving observations with conflicting cloud vs. clear-sky signals, where visible and NIR reflectances are high, but infrared brightness temperatures are relatively warm. Details and examples of new and modified cloud tests are shown and various methods employed to evaluate the new cloud mask results. Day vs. night sea surface temperatures derived from MODIS radiances and using only the MODIS cloud mask for cloud screening are contrasted. Frequencies of cloud from sun-glint regions will be shown as a function of sun-glint angle to gain a sense of cloud mask quality in those regions.

Cirrus clouds have been identified as one of the most uncertain components in climate research. They are located at high altitudes (near the tropopause), are frequently optically thin in nature, and are composed of non-spherical ice crystals. In this paper, we detail a method for inferring tropical cirrus cloud optical thickness from MODIS level-3 derived cirrus reflectance and solar/satellite view geometry data. We then demonstrate the applicability of this method using an independent MODIS level-3 data file from NASA s Aqua satellite to obtain the average daily tropical cirrus optical thickness. A preliminary study has also been conducted to ascertain the general characteristics of tropical cirrus cover as a whole using two consecutive years of Aqua MODIS global daily data. This study includes the frequency of occurrence (percentage of days with cirrus cover) and the spatial distribution of optical thickness fields. The retrieval method described here is complimentary to the standard operational MODIS cloud products (included in level-3 data) for the case of tropical cirrus clouds.

A great need exists amongst X-band direct broadcast regional users for near real-time, high spatial resolution cloud detection and cloud property retrieval to support regional interdisciplinary applications. As part of the International MODIS and AIRS Processing Package (IMAPP), the objective treatment of spatial and spectral information, including principal component and residual techniques, is provided by the AIRS single field of view clear and cloud detection and cloud property retrieval algorithm. This algorithm, known as Minimum Local Emissivity Variance (MLEV), is used to retrieve both cloud height and cloud spectral emissivity. The ECMWF model analysis is used to demonstrate that high quality clear radiances can improve the yield and quality of cloud spectral emissivity and height, quantities that are precursors to retrieving cloud micro-physical properties and cloudy sounding profiles. In this paper we describe in detail the procedure employed to achieve this goal. The use of cloud spectral emissivity and height in retrieving cloud micro-physical properties is discussed together with their utility in identifying cloud contaminated soundings in the IMAPP AIRS only single field of view retrieval.

The University of Hawaii routinely collects direct broadcast MODIS images over Hawaii. Using this data set we process real time satellite images of aerosol optical depths around Hawaii using our custom algorithm. MODIS channels 1 and 2 (~ 645 and ~ 858 nm) are used to derive aerosol optical depth spatial and temporal properties. The use of MODIS channels 1 and 2 provides images with 250 m resolution resulting in improved cloud detection. Due to this improvement, background aerosol optical depths values remain low even in regions of many small clouds. Although cloud rejection is not expected to be perfect, using 250 m resolution data provides a significant improvement over 1 km resolution data. In order to correct for surface reflection, meso-scale wind fields from the Regional Spectral Model (from the National Center for Environmental Prediction) and synoptic scale winds (from National Center for Environmental Prediction) are interpolated to the satellite pixel size. The use of meso-scale wind fields is required for the complex wind fields in and around the Hawaiian Islands. Here we will discuss the aerosols encountered in Hawaii, and provide examples of interesting aerosol optical depth images around Hawaii.

In order to understand the atmospheric constituents over the urban area, the aerosol properties obtained from radiometry with AERONET are compared with the suspended particulate matter (SPM) simultaneously measured with a new instrument (SPM-613D). It is found that the SPM measurements classified as fine particles (PM_2.5) and coarse particles (TSP/PM₁₀) are very useful for determining the dominating of particle size and air quality. There was a strong correlation between the PM_2.5 concentration and aerosol index (AI). It indicates that aerosol characteristics can be estimated from SPM data, and vice versa.

Acquisition of aerosol information on a global scale, especially over the continent, is an urgent task for the better understanding of Earth's radiation budge and climate change. However, it is known that aerosol retrieval over land is much more difficult than that over ocean due to the complication of surface properties. A polarization sensor POLDER boarded on the satellite ADEOS-1 and -2 has shown that the polarization information is useful to extract the aerosol properties such as AOT (Aerosol Optical Thickness), and its wavelength tendency (Angstrom exponent) not only over the ocean but also over the land. Recently the polarization sensor becomes to be noticed. At such a time, this work focuses on role of polarization information from the point of view for aerosol retrieval. As a result, an improved map of aerosol is obtained based on POLDER-2 data. The obtained space based aerosols are examined with the radiometric measurements from the ground.

The Moderate-resolution Imaging Spectroradiometer (MODIS) provides aerosol optical depth (AOD) along with the fine mode fraction over ocean and darker land surfaces. Measurement Of Pollution In The Troposphere (MOPITT) onboard the Terra satellite provides quantitative information of carbon monoxide (CO). Measurements of CO whose principal sources arise from anthropogenic emissions such as biomass burning and forest fires, is very useful for tracing fire emissions in the atmosphere. In this study, intense fires in the southeast part of Russia in May, 2003 are studied with the satellite data from MODIS and MOPITT. The AOD distribution from the MODIS for May, 2003 show stretched regions of high AODs near the Korean Peninsula. The CO concentrations at 700 hPa from the MOPITT for May, 2003 also show enhanced values. Correlation between CO and AOD are investigated for the forest fire case. This multi-instrumental approach to monitor the aerosol in the atmosphere is expected to contribute to the classification of the aerosol characteristics in the atmosphere, carbonaceous aerosol in particular.

Massive smoke plume from forest fires reduced visibility on regional scale in Northeast Asia in May 2003 during boreal forest fire season in Siberia. Smoke aerosol events and their effects are investigated using satellite data from the Moderate Resolution Imaging Spectro-radiometer (MODIS), Measurement of Pollution in the Troposphere (MOPITT), Clouds and the Earth's Radiant Energy System (CERES), and Total Ozone Mapping Spectrometer (TOMS) over Northeast Asia. Extensive forest fires were detected from MODIS fire product (MOD14) data over Siberia. Aerosol optical thickness (AOT) of the smoke aerosol from fires can be retrieved from the MODIS Level 1 data by using the Bremen Aerosol Retrieval (BAER) algorithm. The retrieved mean AOT ranged from 2 to 4 over smoke plume covering Northeast Asia. Over most of the Northeast Asia, CO concentrations was about 3.0 molecules/cm² in this region. The top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) from CERES has been estimated. The mean TOA SWARF was about 130~290 W/m² over smoke aerosol plume, indicating an aerosol cooling effect.

The successor of the Improved Limb Atmospheric Spectrometer (ILAS), ILAS-II, aboard the Advanced Earth Observing Satellite-II (ADEOS-II) measured atmospheric absorption spectra at a wavelength region from 753 nm to 784 nm, including the molecular oxygen (O₂) A-band centered at 762 nm, with a FWHM spectral resolution of 0.06 nm. Temperature and pressure profiles between ~10 km and 80 km were retrieved from the solar occultation measurements of the O₂ A-band spectra during the operational period of ADEOS-II in 2003. Based on the actual measured data during the smallest atmospheric variability, the repeatability of the measurement, which is a measure of the measurement precision, for temperature and pressure was estimated to be 1-2 K and 0.5-2%, respectively. Comparisons between ILAS-II and the U.K. Met. Office (UKMO) stratospheric analyses or the NASA's UARS/HALOE and TIMED/SABER temperature data are performed. Regardless of the good precision, it is found that the ILAS-II temperatures are systematically lower in the stratosphere and significantly higher in the lower mesosphere.

Ozone density profile over the Korean peninsula was obtained by UV radiometer onboard the KSR-III (Korea Sounding Rocket-III) launched in Nov. 2002 and compared with other observations from satellites and ozonesonde. Due to altitude limitations in this first test flight of the newly-developed system, the apogee of the rocket was still in the stratosphere. Most of the previous algorithm for the optical absorption technique assumed to have measurements out of the ozone layer but our situation provided an opportunity to consider an algorithm to retrieve the vertical profiles of O₃ number density for the rocket flight whose apogee is still in the ozone layer. In measurements by using optical instruments, various error sources exist in characterizing optical properties of detectors and atmospheric parameters. The magnitude of errors are analyzed and estimated in various rocket soundings but their quantitative effects of error sources due to each parameter in the retrieval have not been investigated in detail yet. In this paper, the quantitative error effects on the retrieval algorithm are investigated with respect to the altitudes. It is worthwhile to investigate this error sources for the current sounding as well as to reevaluate the previous rocket sounding data. Among retrieval parameters, the most influential error sources are found to be the absorption cross section and the filter response function. +0.65 nm shift in filter response function or -0.55 nm shift errors in absorption cross section are found to result in 5% deviation on the total number density. Whereas the total number density profiles are not so sensitive to the Rayleigh scattering or the slant air column density assumed. The stray light effect of the interference filter was also investigated.

The Clouds and the Earth's Radiant Energy System (CERES) instrument has scanning thermistor bolometers that measure broadband radiances in the shortwave (0.3 - 5.0 micrometer), total (0.3 - >100 micrometer) and 8 - 12 micrometer water vapor window regions. The CERES Flight models I and II (FM1 and FM2) instruments were launched aboard the Earth Observing System-Terra platform on December 1999. The CERES instrument can operate in fixed as well as rotating azimuth positions with the elevation head moving in full scan or short scan modes. The sensor measurements have shown a dependency on observation geometry during each of these scan modes of operation. The zero radiance offsets of the sensors were measured using end caps (low emittance aluminum targets) on the ground at each elevation observation angle in fixed azimuth scan mode. The Terra spacecraft have conducted two sets of calibration maneuvers viewing the deep space on-orbit in March and April 2003. During these tests where the spacecraft is constantly pitched to view the cold space (3 degree K blackbody), zero radiance offsets were measured for the CERES sensors in all scan modes of operation. This paper describes the procedures used to determine the zero radiance scan offsets for CERES sensors. The measured offset values calculated from ground and in-flight tests for the FM1 and FM2 sensors are also presented.

Satellite measurements provide important tools for understanding the effect of mineral dust aerosols on past and present climate and climate predictions. Multi-angle instruments such as Multi-angle Imaging Spectro-Radiometer (MISR) provide independent constraints on aerosol properties based on their sensitivity to the shape of aerosol scattering phase functions. The current MISR operational retrieval algorithm (version 16 and higher) was modified by incorporating new non-spherical dust models that account for naturally occurring dust shapes and compositions. We present selected examples of MISR version 16 retrievals over AERONET sunphotometer land and ocean sites during the passage of dust fronts. Our analysis shows that during such events MISR retrieves Angstrom exponents characteristic of large particles, having little spectral variation in extinction over the MISR wavelength range (442, 550, 672 and 866 nm channels), as expected. The retrieved fraction of non-spherical particles is also very high. This quantity is not retrieved by satellite instruments having only nadir-viewing cameras. Our comparison of current (version 16) MISR-retrieved aerosol optical thickness (AOT) with AERONET instantaneous AOT shows better coverage and stronger correlations than when making identical comparisons with previous AOT retrievals (version 15). The MISR algorithm successful mixtures include a non-spherical dust component with high frequency in retrievals over dark water and slightly lower frequency over land. Selection frequencies of non-spherical dust models also decrease in dusty regions affected by pollution.