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Airborne: The View from Down Under
A small end-user community in Canberra, Australia strives to provide remote sensing solutions for a series of water and forestry applications.
By Mary Jo Wagner Australia may be a country down under, a seemingly quiet region away from remote sensing gossip, but soon it may rightfully gain a central position on the remote sensing industry map. Thanks to a few visionaries, a talented pool of researchers and scientists and one very important piece of technology, Australia may soon be an example for the rest of the remote sensing community to follow.
It's no secret that people both in and out of the remote sensing community are eager to see more commercial applications of the technology developed. Everyone agrees the potential is there for various applications, yet obstacles to achieve that end abound from all directions. The solution? A small end-user community in Canberra, Australia is striving to provide its colleagues just that through a series of highly successful water and forestry applications.
A key to their success has been an "eagle-eyed" instrument officially known as the Compact Airborne Spectrographic Imager, or casi. Produced by the Canadian-based Innovative Technology, Research and Excellence in Science (Itres) Instruments, the casi has been soaring over regions of Australia since 1993.
Ask any Australian scientist who has used the casi for any project, and their response will more or less be the same: "you couldn't do what we did without it."
Since the early '90s, the Commonwealth Scientific Industrial Research Organization's Division of Water Resources in Canberra has been carrying out various water applications projects, studying the water quality of particular river systems and coastal waters, algal blooms and mapping the bathymetry. The casi enabled them to achieve a level of accuracy and detail never before attained using conventional methods says David Jupp, science project leader of CSIRO's Earth Observation Centre.
The Hawkesbury River was the site of one of the most comprehensive optical water quality studies conducted during the Australian '93/'94 summer. The Hawkesbury River Project
The Hawkesbury is used extensively for agriculture, irrigation, sewage disposal and recreation. Most importantly, part of the Hawkesbury Nepean Catchment is the main water supply for the city of Sydney. And over the last decade, the lower-end of the river has had continual water quality problems stemming from ample use.
Despite efforts to clean up the river, the Hawkesbury is still plagued by algae blooms, in particular, blue-green algae, which is highly toxic to fish and animals who drink the water. It can even be harmful to humans. In the summers of '92 and '93, warning signs informed the public to avoid contact with the water because the presence of neuro-toxic cyanobacteria exceeded levels recommended by the Blue-green Algae Task Force.
About the same time that the blue-green algae was wreaking havoc on the Hawkesbury, Graham Harris, former chief of space science for Australia, heard a presentation about the casi at a conference. Intrigued by the results achieved using casi data, Harris arranged to have it brought to Australia. Its first test was the Hawkesbury. The casi
The casi is a pushbroom imaging spectrometer that measures radiation from 400 to 1000 nanometers of the electromagnetic spectrum. Launched by Itres in 1990, the casi is a very portable instrument, and easily installable in a variety of aircraft, such as small jets, twin and single engine aircraft and helicopters. It operates in two modes: the spatial mode where it collects data in 19 bands, and the spectrometer mode which provides 288 continuous spectral measurements at 1.8 nanometer intervals. A fully programmable and calibrated system, the casi has a swath of 512 pixels and its resolution can range from .5 meters to 10 meters.
Combining accurate aircraft movement, GPS measurements and digital elevation models, casi imagery can be fully geometrically rectified. Image data can be viewed in flight and radiometrically corrected immediately upon landing.
But the feature of the casi that most users point to which distinguishes it from other optical airborne systems is its narrow bands, specifically that they are spectrally programmable to suit an application. Users have the ability to choose the wavelength and width of its spectral bands, a feature no other commercial instrument offers today, says Steven Mah, vice president of Itres. The combination of the casi's narrow bands and high sensitivity are what made the casi particularly beneficial to the Hawkesbury project and the other water studies carried out, says Jupp.
The specific objective of the Hawkesbury study was to accurately assess the eutrophic conditions and sediment transport, map the turbidity and chlorophyll levels, and recognize and map different algae types.
The casi was flown in the spectrometer mode at 10,000 feet in March '93 and February '94. Extensive ground truth was done for the '93 mission to create a "library" of water optical properties. Stemming from that resource, in-situ data was not used to map the concentrations for the '94 mission. However, agencies collaborating on the project conducted ground truth and found the maps produced correlated very well.
All of the data was atmospherically corrected, geometrically rectified, mosaicked and inserted into a GIS. A series of maps at a scale of 1:25,000 with a resolution of 5 m were produced, indicating the level of turbidity, sediment and chlorophyll and clearly distinguishing the blue-green algae from different algae types.
Jupp says the casi enabled them to successfully map all the concentrations of interest, even without ground truth, because of the sensitivity of the sensor and the high spectral resolution. That was particularly important in the turbid waters.
"A lot of inland waters in Australia are very turbid and with other instruments that we've used, the signal that we got back was not associated with the water properties," he explains. "So we really needed the sensitivity and the high spectral resolution, and more importantly, the very high signal to noise ratio that you get with the casi to map these properties successfully. I don't think we could've achieved what we did without an instrument of that type."
Adds Harris, "The airborne measurements that we collected at 10,000 ft. were better than what researchers gathered from boats in the river itself. And we did it in much faster time as well."
From the data produced, Jupp and his colleagues were able to map the presence of the toxic algae and monitor its levels, even in areas where levels were low or no blooms were apparent.
"The casi is enabling us to collect measurements from the air that would otherwise be unachievable by laboratory or field methods," concludes Jupp. "It's allowing us to actually take measurements of water properties, not just a picture. That's a big step forward." Port Phillip Bay
The most recent project where the casi has been successfully applied was Port Phillip Bay, a large embayment adjacent to Melbourne about 1950 square km in area. It serves as a major resource for the state of Victoria. Much the same as in the Hawkesbury River, the PPB is suffering from the stress of extensive use, excess nutrients and urban encroachment. Thus a $12 million applied ecology program has been established to assess the water quality of the bay and devise an operational monitoring program.
The casi was used to map the bathymetry of the entire bay and the benthic communities present. The data acquired was compared with a set of water optical measurements to determine the intrinsic water properties and assess the phytoplankton present.
In order to handle the data volumes and lengthy image processing techniques that this plan would produce, Jupp developed a special mosaicking software that allowed the researchers to seamlessly "stitch" together up to 20 individual images at once.
"David's real breakthrough has been to produce a technique whereby you can seam strips together and produce mosaics that look like satellite images but they've got a 5 m resolution and 16 to 32 spectral bands instead of four or five as in satellite imagery," says Harris who is the program manager for the PPB project.
Over a two month period, the casi gathered 73 flightlines, gathering up to 40 km of data in each flight, to produce a uniform and comprehensive mosaic of both the bottom topography of the bay and what types of vegetation reside there.
Through an additional tool that CSIRO developed, researchers were able to indicate and interpret spectral signatures of different algae on the bottom of the bay, under 10 m of coastal waters, and how these signatures were changed by the water column itself, says Alex Held, project leader of the remote sensing group at CSIRO-DWR.
Underwater video transects and diver observations were both carried out to validate the casi imagery, although the correlations between the data sets are yet to be determined.
However, Harris and his team are already quite impressed with the casi and the results of this part of the PPB ecological program.
"We need information at the spatial scales offered by the casi to look at regional development programs, land use, catchment management, watershed management problems and coastal zone water quality problems," Harris says. "And they've got to be looked at at regional scales. The only way to collect synoptic data at regional scales is using airborne instruments. You can't do it with a boat because the water moves, you can't do it from space because the pixel sizes are too big and the spectral quality isn't good enough. The casi instrument fits a very important niche in the market because it has the spatial resolution and it has the spectral resolution to give us spectrophoto measurements of water quality parameters."
In addition to evaluating the casi for water-based applications, the instrument was also used for forestry and agricultural applications as well for two purposes: to evaluate its use for operational management of forest resources and precision farming, and to study vegetation health.
Data was acquired in both tropical forest regions in Indonesia and pine forests at a resolution of 2.5 meters, allowing them to delineate forest boundaries and distinguish individual tree crowns - a monumental task using conventional means.
"Using spectral mixing and classification techniques, we can look at the different crowns and vegetation types in some of the forests in the tropics where every other tree can be a different species," says Held. "That is really powerful. "
They all contend that the casi produced impressive results and exceeded their expectations. They say its spectral and spatial resolution, coupled with its portability offer the greatest benefit to end users.
But the story doesn't end here.
This series of environmental monitoring studies were the "proof of concept" for a much larger plan for the casi: the establishment of a commercial environmental monitoring business in both Australia and Indonesia. It is the type of program that the remote sensing community eagerly strives to attain.
"There is a lot of good science being done in remote sensing, but very little of it is deliberately focused towards solving environmental management problems," says Harris. Thus developing a commercial business became the brainchild of Harris and his colleague John Trippett, a consultant at Asia Pacific Holdings Ltd, four years ago.
The availability and performance of the casi is instrumental to making the program possible. "The vision always was to use the casi as an environmental monitoring tool," Harris explains. "I've always thought that remote sensing was a very important adjunct to the plethora of monitoring techniques available. Our intent was to use the technology to actually solve environmental management problems."
The groundwork has already been laid. Harris has presented the results of the Hawkesbury and PPB projects to key agencies: the Environmental Protection Authority, the Privatized Water Authority and the Department of Conservation and Natural Resources. Operational monitoring programs for water systems may soon become a reality in Australia.
And in Indonesia, a major environmental monitoring and mapping program is underway. Coastal zone sites, some of which are under threat of urban development and deforestation, were flown with the casi in May. Tropical forests are next. About the Author:
Mary Jo Wagner is a freelance writer/editor who writes about GIS and remote sensing. She may be reached at 415-291-8292 (phone) or E-mail: [email protected]
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