| Mapping Hawaii with Digital Aerial Imagery
Aerial imagery provides valuable Hawaiian resource information and challenges traditional approaches.
By Don Light, George Rohaley and Gerry Kinn Hawaii, "The Aloha State," is world-famous for its beauty and pleasant climate. It has deep blue seas with natural harbors, brilliantly colored flowers, graceful palm trees, abundant agriculture, and massive mountains with plunging waterfalls that flow into deep canyons and fertile valleys. Hawaii consists of a 1610-mile long chain of 122 islands. The eight main islands are at the southeastern end of the chain where Hawaiians live on only seven of these main islands. Tourism, military bases, and agriculture represent the largest sources of income. More than a third of the world's supply of pineapples comes from the plantations that dot the fertile valleys, along with sugar cane, bananas, coffee and other crops. Need for Image Information Anyone who has been to Hawaii agrees that it is truly an island paradise. However it's almost continuous and heavy rainfall (up to 460 inches per year in the mountains) is a formidable challenge to resource managers who need up-to-date aerial imagery to map the islands. "Both USDA's Natural Resources Conservation Service (NRCS) and the Farm Service Agency (FSA) conduct most of their business through the use of imagery, whether for the production of soil surveys, crop inventories, natural resource inventories, conservation planning for farmers and ranchers, watershed planning, or wildlife habitat projects. Remote sensing technology can provide the essential imagery ingredient for resource management. The USDA's implementation of Geographic Information Systems (GIS) in daily operations makes digital imagery essential and we cannot operate effectively without it," said Dr. Chris Smith, NRCS state soil scientist in Hawaii.
In fact, for the past two decades, managers of the USDA's Natural Resources Conservation Service (NRCS), Farm Service Agency (FSA), Forest Service (FS), and the National Agricultural Statistics Service (NASS), worked with Federal and State agencies in an attempt to acquire new imagery for Hawaii, all without success. They had tried a variety of acquisition options including contracting through the National Aerial Photography Program (NAPP), commercial satellite imagery, and even seeking approval to use National Technical Means at a degraded resolution. The major difficulties for flying imagery in Hawaii include the unstable weather patterns, mainly because of clouds and wind, and extreme terrain elevation differences across each of the eight islands.
"High-resolution imagery has been extremely difficult to obtain. The major reasons for this are the presence of trade-wind-derived convection clouds that materialize about 9:00 a.m. nearly every day over the mountains. These clouds back up, too, and spill over the crests onto the lee sides. While creating our famous rainbows, it plays havoc with any aerial imaging flight plan," adds Smith. The weather and terrain differences between mountains and lowlands, coupled with the sheer distance for smaller aircraft to travel from the mainland, caused most contract proposals to exceed agency budgets for buying imagery. USDA Looks to the Private Sector
FSA and NRCS put together a funding package to produce Digital Ortho Quarter Quads (DOQQs) for the entire State. Funding from other sources was solicited, but none was available. On behalf of the FSA and NRCS team, the FSA Aerial Photography Field Office (APFO) issued a Request for Proposals (RFP) calling for 496 CIR DOQQs in the UTM projection cast on the NAD 83 datum to cover all eight islands. The resolution will be one meter, and the output will be on CD ROM acceptable as input to GIS. The USDA team was composed of George Rohaley, remote sensing leader for NRCS, and Glenn Bethel, chief of the FSA Remote Sensing Section, along with Ronald Nichols, director of the FSA APFO and Geoff Gabbott, contracting officer FSA APFO. Acquiring DOQQs for Hawaii complements the NDOP goal to complete nationwide coverage of the entire United States. With this in mind, the RFP was prepared so that vendors could select the tools to meet the requirements, thus allowing for the prospect of an innovative solution. Introducing Emerge, Landcare Aviation, and PAR Government Systems
In business since 1997, Emerge (Billerica, Mass.) and its aerial services contractors won the contract by proposing their high-tech Direct Digital Imaging System. Landcare Aviation (Oriskany, N.Y.) is providing all aerial imaging flight services, and PAR Government Systems (Rome, N.Y.) provided DOQQ formatting and an added level of quality checking. Emerge, through Landcare Aviation, has eight Cessna 172s and two Piper Aztec aircraft committed to Emerge business interests across the country. Each of the ten aircraft have the Emerge Direct Digital Imaging System, composed of a Kodak DCS 460 Digital Camera, integrated with Kinematic GPS and a precision Litton 200 Inertial Measuring Unit (IMU). Direct Digital Imaging is gaining acceptance in the mapping community because the image data can be orthorectified and geopositioned, given a suitable DEM, without the need for aerotriangulation and ground control-a real savings in time and cost. In addition to the geometric advantages, the digital system can often acquire acceptable imagery by flying under full cloud cover.
Once the imagery is collected, it is sent via FedEx to the Emerge factory in Billerica, where geometric and radiometric corrections are performed, and the best available digital elevation model is utilized for orthorectification. All products are orthorectified and georeferenced, and the color-balanced mosaic is then sent to PAR Government Systems for formatting into a DOQQ according to National Digital Ortho Photo (NDOP) standards. The finished DOQQ on a CD ROM (150 MB) will meet National Map Accuracy Standards (NMAS) at 1:10,000-scale, which results in less than 8.5 meters pixel placement error, with 90 percent Circular Error Probability (CEP). Recent control range fly-overs have resulted in CEPs of 4.1 meters and 2.0 meters when compared to ground control. Additional tests are planned to further validate the accuracy. Achieving CEPs under five meters speaks well for direct geo-referencing. Mission Challenges
Meeting the challenges of the Hawaii project represents a major milestone for Emerge. Al Stringham, president of Landcare Aviation, Inc., stated, "This is our first effort outside continental U.S. The constant cloud cover is a major challenge, since we can't wait for a clear day to cover a large area with one flight. Instead, the aircraft goes up almost daily looking for temporary clear areas not previously flown and large enough to contain at least one Quarter Quad." This tenacious approach is a distinct departure from traditional mission planning, where you wait for a perfect weather day to get a large area in one flight. Preparing for the Flight to Hawaii
Landcare chose one of its twin-engine Piper Aztec aircraft to make the 2200 mile flight over the Pacific Ocean to Hawaii. A ferrying company in Oakland, Calif., was chosen to prepare the plane and fly it to Honolulu, an awesome trip for a small aircraft. Landcare delivered the aircraft to Oakland in early December 1999. To reduce aircraft weight, the sensors were removed and shipped separately, leaving more room for extra fuel to make the trip. The ferrying company installed temporary internal fuel tanks so it could make it to the islands, given favorable winds. They waited for the proper winds and took off for Honolulu during the third week of December 1999. Things were progressing according to plan until about 650 miles out, when the winds shifted and the pilot had to turn around and return to California. Another few days went by until, on December 24, the winds were favorable for the pilot to take off again for Honolulu. Thanks to good weather and winds, the pilot landed the Aztec safely at the Honolulu Airport, early on Christmas morning
The LAI pilot and ferry pilot removed the auxiliary fuel tanks on Christmas day. LAI personnel then reconfigured the Aztec and installed the Emerge sensor package. They reinstalled the camera, the GPS receiver, and the IMU so the plane was ready to overfly the newly established calibration range. Emerge engineers had previously established a calibration range by GPS ground surveys and located a GPS base station on Oahu. The calibration imagery was flown, the sensors were aligned and re-calibrated, and real flights for CIR DOQQ imagery began in late January.
From that point forward, progress was in the hands of the pilot, the weatherman and Nature, but possibly not in that order. Each morning, the pilot checked the weather and headed to collect imagery. The pilot followed a prepared flight plan so that all quadrangles will be covered. As of April 15, 2000, the team has collected about 25 percent of the imagery for the 496 DOQQs.
"This project will provide the basis for creation of a digital, seamless, one-meter CIR view of the state of Hawaii. The new base will allow for better ways to link producers with their land, and with USDA farm programs. Also, the delivery time from data acquisition to having a usable product in the field should be much faster than with traditional film-based DOQQ projects. It was great to see the private sector step up to the challenge," says Glen Bethel. The Sensors
Emerge's patented Digital Sensor System consists of three major subsystems. The sensor head includes a Kodak DCS 460 digital camera and a Litton LN 200 fiber-optic IMU. The camera and the IMU are rigidly attached and look out the camera opening in the bottom of the aircraft. Control of data flow and precise timing (0.1 millisecond) is accomplished with the Sensor Management System. The Sensor Management System also houses the dual-band GPS receiver and provides power to the three sensors. Data is stored on a hard drive mounted in the data storage rack, ready for offloading to high-capacity JAZ drives (18 MB per frame) or tapes after landing. The three sensors comprising the Emerge digital data acquisition systems depend on precise time and the integration of the three data sets to position its products to NMAS. This concept is called direct georeferencing. Geometric calibration of the camera was accomplished by using the Multicollimator at the U.S. Geological Survey. The digital camera's major difference, compared to a standard aerial film camera, is the small size of its format and the corresponding smaller ground coverage per frame. Also, since it is all-digital, there is no film to process. The Emerge mosaicing program digitally stitches the frames together and balances the color so there is no evidence of cut lines apparent to the user. Summary
The USDA agencies NRCS and FSA have truly come into the geospatial digital era with this venture. With this technology, photogrammetry continues its transition into the digital era. The digital imager and its associated navigation data impact the collection and production techniques for DOQs. For the next few years, users will continue to have a choice of analog or digital, because both technologies have their respective merits. But the technology is slowly but surely moving toward digital. And while these resource agencies in Hawaii are on the cutting edge of technology, more importantly, they are satisfying their information requirements by saving program funds and not sacrificing data accuracy or quality. About the Author:
Don Light is Manager of Business Development for Landcare Aviation, Inc., Rochester, N.Y. He can be reached at: 716-368-9867 or e-mail: [email protected]. George Rohaley is National Geospatial Remote Sensing Leader for USDA Natural Resources Conservation Service, Beltsville, Md. Phone: 301-504-2268 or email: [email protected]. Gerry Kinn oversees mapping sciences activities at Emerge, Billerica, Mass. Phone: 978-262-0653
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