Cooperative Institute for Research in Environmental Sciences

The development of remote sensing of the Earth over the last 30 years has been heavily dependent on the creation of new tools for data acquisition and analysis. The value in remote sensing for the study of the Earth depends on the revelation of details not visible to the human by other means. These details are manifested in scale, temporal analysis, both intra-seasonal and decadal, spectral sensing in regions beyond the narrow wavelength region accessible by eye, from the near infrared to the microwave, and in the radiometric quality. Not to be overlooked are the data analysis tools without which information could not be derived from the data. Tool development has been a major component in Goetz's research effort.

Multispectral imaging, acquiring black and white images in fewer than 10 spectral bands at once, has been the mainstay of the NASA remote sensing effort beginning with the first Landsat satellite in 1972. Multispectral imaging allows the separation of different land cover types into thematic classes, or mappable units, based on differences in spectral reflectance or spectral emittance in the thermal region of the spectrum. At NASA-JPL, beginning in 1980, Goetz spearheaded the development of a new type of instrument called an imaging spectrometer. With imaging spectrometry it is possible to collect data in hundreds of registered, contiguous spectral bands so that for each picture element a complete radiance spectrum can be obtained. With proper correction for the intervening atmosphere, it is possible to derive a complete reflectance or emittance spectrum from the radiance. The spectra are equivalent to those obtained with spectrometers in a chemical laboratory for material identification. In 1990, the military and intelligence community became interested in the technique and renamed it hyperspectral imaging.

Beginning in 1989, Goetz received a $50 million contract to support the development and operation of the High Resolution Imaging Spectrometer (HIRIS) to be flown on an Earth Observing System mission, later called TERRA, launched in 1999. As part of a restructuring and severe budget cut for the project in 1991, NASA dropped HIRIS from the payload and only a small portion of the $50 million was spent in CSES. However, it led to several tools and techniques that play an important role in remote sensing today.

Imaging spectrometers produce copious quantities of data. The NASA-JPL instrument Airborne Visible Infrared Imaging Spectrometer (AVIRIS) that flies on the er-2 aircraft at 65,000 feet altitude creates 15,000 224-wavelength spectra per second. In 1989, computers were just becoming powerful enough to begin the thorough analysis of the data. A single 600 x 512 pixel AVIRIS image required approximately a month to analyze. Today, a similar analysis can be done in less than a day. The development of the software to analyze images with hundreds of spectral bands, called SIPS, was first done in CSES by Joe Boardman (Ph.D. 1991), Fred Kruse, Adam Lefkoff, and Kathy Kierein-Young (Ph.D. 1995). This group petitioned the University to allow them to continue development of SIPS into a stand-alone software package for commercial sale after NASA cut the HIRIS funding. They were highly successful and created ENVI, a recognized standard in the remote sensing field. In 2000 they sold the rights to the software to Kodak and continue their consulting services in Boulder as Analytical Imaging Geophysics, LLC. The development of ENVI is recognized as a key element in the application and exploitation of hyperspectral imaging data for the study of the Earth.

In 1988, Bo-Cai Gao joined CSES as a research associate after receiving his Ph.D. in physics from Ohio State University. Gao went to work on the problem of removing the effects of water vapor and aerosols from hyperspectral images based on the image data alone. This technique was critical, since it would not be possible to make ground-based measurements during every overflight and, as we would later learn, total precipitable water vapor values can vary rapidly across an image. Gao was successful in creating ATmospheric REMoval (ATREM), a program that has been standard for the last 10 years. He also discovered a technique for detecting cirrus clouds over land by observing in the deep 1.4 µm water absorption feature and developed a technique for determining cloud height based on mapping the total precipitable water vapor. The spectral bands required for water vapor mapping and cirrus cloud detection were subsequently incorporated in the MODIS instrument that images the whole Earth every two days as part of the TERRA mission. Gao moved on to NASA Goddard and thence to the Naval Research Lab. More recently, a new atmospheric removal program that provides more accurate results has been developed by Zheng Qu, a research associate with a Ph.D. from the University of Chicago. The program called HATCH makes it possible to correct pushbroom imaging spectrometers such as the hyperspectral imager Hyperion on the EO-1 mission.

As part of the HIRIS program, Goetz and Curtiss developed the first lightweight, fully portable field reflectance spectrometer for validation of satellite and airborne spectral imaging. When the NASA program manager refused to support further development of the field instrument, Goetz and Curtiss founded Analytical Spectral Devices Inc. (ASD) to further develop, manufacture and market portable field instruments. Field- Spec instruments are now the standard in the remote sensing research field and are found in 35 countries.