ENVI Used to Detect Pollutants in Houston
Anonym
Customer Challenge
The City of Houston was looking for a way to detect illegal or unauthorized chemical releases or disposal of them on land, in the air or in the water. Their vision was to use hyperspectral imagery to detect, measure and identify pollutant discharges and emissions. Once the detection and measurement had taken place, their ultimate mission would be to help enforce local, state and federal regulations and apply the data as an enforcement tool.
Solution Achieved
As Americans become more environmentally aware, and scientists present concrete proof about the adverse effects of pollutants to our atmosphere, land, water and subsequently our health, it is increasingly important to enforce laws meant to stop the spread of harmful chemicals. In the past, agencies tasked with enforcing laws and regulations had a steep hill to climb. Detecting the presence of pollutants and chemicals was difficult, and proving what, where, and how something entered the environment was nearly impossible.
Now, through the use of remote sensing technology, and programs such as ENVI®, GIS imagery analysts from the City of Houston Environmental Health Division can detect the presence of illegally discharged chemicals by their spectral signatures, and track them back to the point of origin to enforce local, state and federal laws.
The scientific community has used remotely sensed data from aircraft and satellites to identify materials on the Earth’s surface for decades. Remote sensing allows researchers and scientists to analyze areas without actually having to be on site. More recently, using remotely sensed data to analyze the spectral properties of materials is a viable option in applications from resource management to agriculture and mining. Identifying materials via their spectral signatures allows analysts to locate and identify different features in data, such as minerals, rocks and chemicals, by means of comparing their spectral signatures with “libraries” of known signatures.
In recent years, a new generation of reasonably cost-effective hyperspectral sensors has been introduced. These sensors produce much more spectral information and higher spatial resolution than traditional remotely sensed imagery sources in panchromatic, or multi-spectral formats with 2 foot to 30 meter spatial resolution. The additional spectral information provides the data needed for the identification of numerous substances based upon their reflectance signature and the higher spatial resolution allows the identification of specific features on the ground facilitating near pinpoint identification of the source and extent of the contamination. ENVI boasts the most robust suite of hyperspectral analysis capabilities available in an easy-to-use package, and is the ideal tool for visualizing, analyzing and presenting this type of data.
The Houston Department of Health and Human Services, led by senior GIS Analyst Larry York, wanted to utilize hyperspectral imagery to facilitate their inspection responsibilities, monitor the environment, and reduce the costs associated with using satellite imagery. Historically, image acquisition was costly, prohibiting experimental uses. Additionally, the available low resolution, multispectral data limited analysis to wide areas, unlike high resolution hyperspectral imagery, which is far more useful in a complex urban environment.
In York’s ground-breaking solution, a project carried out and funded jointly with the Environmental Protection Agency, York’s team borrowed a City of Houston Police helicopter, which they equipped with a leased hyperspectral imaging instrument called AISA. They sent the helicopter on seven flight lines over the Houston Ship Channel to detect, measure and identify illegal land and water pollutants. They chose the areas of interest because of extensive industrial production and suspicions that chemical spills and unauthorized emissions were occurring there.
Once the data were collected, team members used ENVI’s built-in spectral analysis tools, including spectral profiling, spectral plotting, and its Spectral Angle Mapper (SAM) to analyze the flight data for the presence of illegal discharges. The data quickly returned spectral information identifying twenty-five different spectral signatures, which they used to compare to known signatures of chemicals and materials in ENVI’s extensive spectral libraries.
After classifying and plotting the data, York’s team quickly discovered illegally dumped solvents, as well as petroleum products including diesel fuel, and paint. They then used ENVI to create detailed maps of the chemicals and intuitive visualizations to present their findings.
By zeroing in on the illegal pollutants, York can now immediately send personnel to a site to perform ground truth testing. Before this method was devised, finding the pollutants and identifying them was a shot in the dark, a process made even more difficult when chemicals dissipated quickly in the atmosphere before identification. “Without ENVI, this project never would have happened,” said York. “We could have collected the data, but we also needed an application that could process that data effectively.”
As the cost of leasing or owning a hyperspectral imaging instrument becomes more reasonable, York and others at the City of Houston hope that departments around the country find the funding to use the technology for similarly innovative reasons.
Key Benefits
- The City of Houston was able to accurately analyze hyperspectral data from sensors aboard a COH police helicoptor using ENVI
- ENVI's hyperspectral data analysis capabilities gave the City of Houston the tools they needed to identify pollutants from the air
- ENVI has superior spectral data analysis and classifications tools compared with other software solutions.