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We present further development of our analysis algorithm for Multi-Filter Rotating Shadowband Radiometer (MFRSR) data. The new additions include techniques allowing us to retrieve spectral aerosol single scattering albedo (SSA) and column amount of precipitable water vapor (PWV). The SSA retrievals employ MFRSR measurements of both direct normal and diffuse horizontal irradiances. We present a sensitivity study indicating dependence of SSA retrievals on optical thickness and other aerosol parameters. Influence on the retrievals of a possible error in separation of the direct and diffuse irradiances by the instrument is discussed. The algorithm has been tested on a long-term dataset from the local MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). Our results are compared to AERONET's almucantar retrievals of SSA from CIMEL sun-photometer co-located with the MFRSR at the SGP Central Facility. A constrained variant of the algorithm (assuming zero nitrogen dioxide column values) is used for this comparison and to study the influence of the uncertainty associated with this atmospheric gas on the retrieved aerosol absorption properties. Precipitable water vapor column amounts are determined from the direct normal irradiances in the 940 nm MFRSR spectral channel. HITRAN 2004 spectral database has been used to model the water vapor absorption, while a range of other databases (HITRAN 1996, 2000, ESA) is used in the sensitivity study. The results of the PWV retrievals for SGP's MFRSR network are compared with correlative measurements by Microwave Radiometers (MWR), GPS stations, AERONET, and MODIS satellite product. In the latter case an interpolation technique has been used to determine spatial structure of water vapor field from the network data and to create a 2D dataset comparable with satellite data.

We recently developed a new version of our analysis algorithm for Multi-Filter Rotating Shadowband Radiometer (MFRSR) data that allows us to retrieve fine mode and coarse mode aerosol optical thickness as well as the effective radius of the fine mode. Our retrieval products also include time series of column amounts of ozone and nitrogen dioxide. The algorithm has been tested using a multi-year dataset from the local MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). Here we present an overview of the retrieval algorithm and validate its performance through comparison of our MFRSR retrieval products with the corresponding AERONET almucantar retrieval results derived from a CIMEL sunphotometer co-located with the MFRSR at the SGP Central Facility. A constrained variant of the retrieval algorithm (assuming zero nitrogen dioxide column values) is described in detail. We use this variant of the algorithm to derive the range of physically justified values of the fine mode effective radius and for comparison with AERONET particle size retrievals. A multi-instrument, multi-year, MFRSR dataset from the SGP Extended Facilities is used to examine geographical and seasonal variability of aerosol properties. We find a correspondence between the geographical variation in fine mode particle size and aerosol composition (nitrates vs. sulfates) as measured by National Atmospheric Deposition Program. A similar correspondence in terms of temporal variability exists between our retrievals and in-situ measurements of aerosol composition made by NOAA Pacific Marine Environmental Laboratory (PMEL) at SGP Central Facility.

In this paper tradeoffs between speed and accuracy for the atmospheric correction of hyperspectral imagery are examined. Among the issues addressed are: the use of scattering calculations on a sparse spectral grid and consequent accuracy and speed tradeoffs; methods of minimizing the required number quadrature points in multiple scattering calculations; effects of the vertical profiles of aerosols and absorbing gases on atmospheric correction; and efficient approaches from including the effects of sensor variability, or imperfections, on atmospheric correction.

We present results from a preliminary analysis of the multi-instrument MFRSR dataset from ARM CART (SGP) site Extended Facilities (Northern Oklahoma and Southern Kansas). Single-instrument retrievals are performed using our previously reported direct-diffuse algorithm. Retrieval products include daily time series of the aerosol optical depth, column mean aerosol particle size, NO 2 and ozone column amounts. The distribution of MFRSR sites at the SGP (central and extended facilities) allows us to combine the retrievals from the individual instruments into series of 2D images. These 2D images facilitate the investigation of spatial and temporal variability of aerosols and trace gases. These images can be also used to evaluate satellite aerosol data products (e.g. MODIS, TOMS, EO-1).

The Multi-Filter Rotating Shadow-band Radiometer (MFRSR) makes precise simultaneous measurements of the direct solar beam extinction, and horizontal diffuse flux, at six wavelengths (nominally 415, 500, 615, 670, 870, and 940 nm) at one minute intervals throughout the day. MFRSR data obtained at tens of sites throughout the U.S. has been available for several years. This is a potentially very important but as yet underutilized data set. We describe and validate a retrieval algorithm for processing of MFRSR data from clear and partially cloudy days. This method uses consistency between direct normal and diffuse horizontal measurements together with a special regression technique to retrieve daily time series of column mean aerosol particle size, aerosol optical depth, NO2 and ozone amounts together with the instrument's calibration constants. Our validation studies demonstrate two advantages of our approach compared to the traditional Langley calibration method: less calibration variability and less sensitivity of retrievals to calibration accuracy. This method is currently used for processing data from a growing number of MFRSRs spread throughout the U.S. determining both time and geographic variability of aerosol properties and gaseous column amounts. This method makes the relatively inexpensive and automatic MFRSR an important tool in climatological research.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper we discuss the possible effect of nonsphericity of solid tropospheric aerosols on the accuracy of aerosol thickness retrievals from reflectance measurements over the ocean surface. To model light-scattering properties of nonspherical aerosols, we use a shape mixture of moderately aspherical, randomly oriented polydisperse spheroids. We assume that the size distribution and refractive index of aerosols are known and use the aerosol optical thickness 0.2 to computer the reflectivity for an atmosphere-ocean model similar to that used in the AVHRR aerosol retrieval algorithms. We then use analogous computations for volume- equivalent spherical aerosols with varying optical thickness to invert the simulated nonspherical reflectance. Our computations demonstrate that the use of the spherical model to retrieve the optical thickness of actually nonspherical aerosols can result in errors which, depending on the scattering geometry, can well exceed 100%.