Printer Friendly

Research Systems' Software Used To Identify Aerosol Pollution In The Northeast U.S.

Business Editors & Technology/Science Writers

BOULDER, Colo.--(BUSINESS WIRE)--May 8, 2001

Research Systems' ENVI and IDL software is being used by researchers at Washington University in St. Louis, Missouri, to study how atmospheric aerosols affect climate change.

Research Systems, Inc. (RSI), is a leading developer of technical data analysis software and a wholly owned subsidiary of Kodak. This research is focusing on mounting evidence that atmospheric aerosols could partially neutralize the heating effect of greenhouse gases. Dr. Fang Li, senior research associate, and Professor Rudolf Husar, are taking a novel approach to aerosol pollution research. Using ENVI they have proven that SeaWiFS (Sea-viewing Wide Field-of-view Sensor) satellite data, typically used for the study of the Earth's waters, can be successfully used in cloud-free areas over both water and land in the study of aerosol pollution. SeaWiFS is the NASA name for the OrbView-2 sensor owned and operated by Orbital Imaging Corporation, of Dulles, VA.

Aerosols are typically studied over water, due to the relatively constant reflectance of water and the ability to easily separate surface and atmospheric contributions on the satellite signal. The remote sensing of atmospheric aerosols over land, however, is still a challenging issue. The influence of surface reflectance over land is much more complex on a satellite signal, which makes it difficult to separate the surface and atmospheric contributions. Their 30-day pilot study has shown the existence of large, 1km by 1km scale hazy air masses with strongly varying spectral extinction -- a measure for aerosol attenuation to sunlight -- which could be a sign of aerosol pollution, and has demonstrated that the methodology is potentially applicable for daily, global monitoring of aerosols and surface color over cloud-free areas.

Dr. Li and Professor Husar's primary goal is to extract atmospheric aerosol information -- particulate matter air pollution -- in the Northeastern region of the United States in an effort to identify the existence of aerosol pollution in that area. "Standard remote sensing techniques provide only the combined surface and aerosol reflectance, but not their separate contributions," explains Dr. Li. "We are focusing on a unique technique called co-retrieval. The challenge of co-retrieval is to separate the aerosol and surface reflectances in order to have 'truer' measurements of both." Their project is based on a radiative transfer theory that states that sensed radiation is decomposed into scattering and absorption by gases and aerosols, as well as reflection from surfaces and clouds, and that air scattering and surface/aerosol reflectance are assumed to be additive. The co-retrieval process entails several steps. First, one removes air scattering and absorption from the satellite images. Second, long-term data are used to generate aerosol and cloud-free surface images. Third, the initial aerosol properties are estimated over non-cloudy areas. Fourth, the aerosol is derived for each pixel based on an excess reflectance. Lastly, daily aerosol-free surface reflectances are reconstructed, and the aerosol properties are updated.

Although the retrievals of aerosol and surface reflectance are interdependent, and provide a mutual quality control through iteration, successful aerosol retrieval depends on high-quality surface reflectance data, and the surface reflectance can only be retrieved for known aerosol-optical properties. For Dr. Li and Professor Husar's research, the retrieved aerosol parameters are the columnar aerosol optical thickness at several wavelengths, such as .416 and .67 um, and the spectral aerosol reflectance function. Both the aerosol parameters and the surface reflectance are retrieved over all cloud-free areas at all wavelengths. Dr. Li and Professor Husar use eight wavelength (0.4-0.9 m) SeaWiFS LAC satellite data to co-retrieve both the columnar aerosol optical properties and the aerosol-free surface reflectance. Columnar aerosol optical properties are aerosol optical properties integrated with respect to the height from the ground surface to the top of the atmosphere. The properties indicate the quantity of aerosol load that exists in the entire atmospheric layer. Then, they separate the aerosol reflectance, the air molecular reflectance, and the surface reflectance from the satellite-measured total reflectance.

Dr. Li is primarily interested in the spectral aerosol optical thickness, and spectral surface reflectance. "Spectral aerosol optical thickness indicates how large the aerosol Angstrom exponent is," explains Dr. Li. "Usually, the larger the Angstrom exponent is, the smaller the average aerosol particle size is." Spectral surface reflectance allows him to measure ground biomass.

In addition to SeaWiFS data, Dr. Li and Professor Husar also use WMO visibility data and GIS datasets. WMO visibility data are visibility records collected by the World Meteorological Organization from the meteorological stations and some airports throughout the world. They use the visibility data as a reference index of air pollution to compare the atmospheric aerosol optical properties measured on ground and from space. If there are unique properties, the visibility information is a critical element of most radiative transfer models used in satellite atmospheric correction. The GIS datasets used are ArcView Shape Files, which provide geophysical border information that is overlaid on the ENVI image for a map-formatted output. Dr. Li used IDL to write the data processing routines for the analysis of the SeaWiFS data. He uses ENVI for the data processing and image analysis. Although Dr. Li typically works with data sets that range from 30 to 50 MB, it is not uncommon for him to work with SeaWiFS processed data as large as 130 GB.

Using ENVI, Dr. Li was able to develop a technique called the "cloud screen approach." "The cloud screen approach is based on the at-sensor spectral reflectance," explained Dr. Li. "Cloud spectral reflectance is in flat shape and has high absolute value for each band. We set both the spectral slope threshold and band absolute value threshold to filter the cloud pixels in images." Dr. Li considered other packages before choosing ENVI, but none measured up to ENVI's power and flexibility. "We looked at SeaDAS, which is a freeware package supported by the NASA ocean biochemistry program specifically designed for the analysis of SeaWiFS data. However, it is only available on sgi and Sun platforms, and we needed a more platform-independent solution. Two features convinced us to buy ENVI. One is that it easily displays SeaWiFS data in gray scale as well as RGB. Another is that there is great flexibility for users to manipulate image datasets and render them. I really appreciate ENVI's flexibility in input and output files," said Dr. Li. "Also, we could not display so many images in different band combinations, nor show the x, y, z, profiles as easily, without ENVI."

Dr. Li uses the Building Geometry File routine and Georeference HDF SeaWiFS Data routines the most. "The former is used to produce the satellite viewing zenith and azimuth angles, and solar zenith and azimuth angles. The latter allows us to register the image into the proper latitude and longitude coordinates," he said. "The ENVI z-profile feature is also very important to us. We use it to recognize the spectral reflectance characteristics of vegetation, seawater and cloud, so that we can create the filter of cloud. Gray and RGB arbitrary band selections enable us to find that the bands seven and eight are only minutely influenced by atmosphere, so their corresponding images can be used to distinguish the boundary of the ground surface between sea and land," he said. "ENVI has been very instrumental to us. It is a very powerful and effective image-processing package in the field of remote sensing. It is very good at rendering color images in a flexible way, and does so very quickly. It also allows users to develop their own interfaces, which is a great benefit for someone like me. I look forward to using ENVI in the next stage of this project, and in future remote sensing projects."

About Research Systems, Inc.

Research Systems, Inc., is a wholly owned subsidiary of Kodak that supports more than 200,000 users of its data analysis and visualization software products worldwide through a direct sales force in North America and subsidiaries in France, Italy, and the U.K. All other countries are managed through a network of international distributors. Primary markets for the company's products are engineering, earth sciences, aerospace, medical, agriculture, automotive, oil and gas, and remote sensing. Additional information can be found at

For more information about this press release, please contact Matthew Powell at or 303/413-3906.

IDL and ENVI are registered trademarks of Research Systems, Inc. All other trademarks are the property of their respective owners.

Image Available Upon Request:

Image Caption: SeaWiFS-measured reflectance image after Rayleigh correction, in the Northeast United States on July 16, 1999.
COPYRIGHT 2001 Business Wire
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2001, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Publication:Business Wire
Geographic Code:1USA
Date:May 8, 2001
Previous Article:Cisco Systems Reports Third Quarter Earnings.
Next Article:ADVISORY/New Generation Films Debuts DVD-Quality Internet Video at Cannes Film Festival.

Related Articles
Haze clouds the greenhouse.
Nature fouls Mexico City's clean-air effort.
Polluted air chokes northern Indian Ocean.
Giant pollution cloud hovers over Asia.
Pollution Keeps Rain up in the Air.
Pollution in India may affect climate.
Study Investigates Association of Air Pollution and Health Effects.
The air that's up there: atmospheric scientists focus on nature's role. (Cover Story).
MODIS operandi for mapping haze.
Air pollution impairs lung development in children.

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters