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National Mapping Programs are Affordable Again
Garth Lawrence and Marc Wride
Intermap Technologies
400 Inverness Parkway Suite 330
Englewood Colorado
303 708 0955
glawrence@intermaptechnologies.com
mwride@intermaptechnologies.com
Abstract
It has been many years since governments have undertaken national mapping programs with new, up-to-date source materials. Most national programs are limited to reworking existing data or up-dating only a small fraction of the national dataset each year. As a consequence, most national maps are out of date. As well, because of the cost to produce new, more detailed contour data, contour detail and/or accuracy is insufficient for today’s needs.
This paper describes new national mapping programs undertaken with private sector funding and using interferometric synthetic aperture radar (IFSAR) technology to provide highly accurate yet cost effective data. These are called NEXTMap programs. IFSAR technology with its ability to map at night and through clouds reduces time and costs while providing significantly improved accuracy. IFSAR technology provides an economical means of revising and maintaining a country’s topographic database. The combinations of low cost and high performance will not only meet governmental mapping needs but also promises to have significant impact on civil and commercial users. An operational methodology that successfully makes, accurate map products for the commercial and public market sectors is described.
NEXTMap Britain, Jamaica, Puerto Rico and Indonesia represent nation wide mapping programs where new source data is provided by proven IFSAR technology. Intermap Technologies used its proprietary IFSAR systems to provide detailed mapping data for each of these countries. The technology provides imagery with 1.25m pixel size and 3m horizontal accuracy. A digital surface model is collected with the image. The DSM has data points every 5m that are accurate to 3m horizontally and 1m (3m option) vertically. TerrainFitÒ, software designed to remove the effects of trees and buildings, provides a digital terrain model (DTM) of the ground surface.
With today’s cut backs in government funding, NEXTMap programs can be lead by private industry and be available to governments at reduced costs. This paper describes the NEXTMap national mapping programs and the products created from the data.
Introduction
The geographic mapping industry has widely acknowledged that the accuracy and timeliness of national maps have traditionally been poor. Even more troublesome is that the high current cost of data acquisition is restricting efforts by government agencies to effectively update this critical national resource. Existing out-of-date and inaccurate base maps are impacting the utility of national map data in not only traditional mapping applications, but also emerging applications including air and ground navigation systems, 3D visualization products and in orthorectification of airborne and satellite imagery. The high costs of traditional mapping techniques are restricting efforts of local and national governments in updating these maps on a nationwide level. The introduction of a nationwide geospatial data set including a seamless image layer with a resolution of 1.25 meters, and a seamless DEM with a posting of 5 meters, would permanently change the industry landscape.
Traditional photogrammetric mapping technologies are being challenged by high resolution Interferometric Synthetic Aperture Radar (IFSAR) systems. The first rigorous assessment of IFSAR for topography mapping was demonstrated in 1963. Ten years later, the IFSAR technology has advanced to the point where airborne systems are capable of accuracies in the centimeters. The flexibility of IFSAR system deployment (day or night operation), near weather-independent data collection, cloud penetrating capability, and quick turn-around time is providing an alternative to the conventional photogrammetric technology.
Intermap Technologies is the world’s leading IFSAR (Interferometric Synthetic Aperture Radar) remote sensing imagery and elevation data products, company and a leader in the generation of cartographic and other mapping products. Using its IFSAR technology, Intermap has conducted national mapping programs under its NEXTMap banner for Britain, Indonesia, Jamaica, Vanuatu, The Solomon Islands and Puerto Rico
Figure 1: IFSAR derived DEM for the cloud covered country of Jamaica.
The Need for Improvement
The need for improved remote sensing technologies that can quickly determine accurate terrain elevations over large areas evolved from military requirements. Operational requirements dictate the need for an all (reasonable) weather, day/night, high-speed collection and processing capability. To address these needs, the United States Defense Advanced Research Projects Agency (DARPA) initiated a program in 1993 to develop operational airborne IFSAR capability. Intermap acquired this technology in 1997
In response to DARPA’s mandate to ensure commercial utilization of the technology, Intermap invested several millions of dollars in the IFSAR technology. Intermap, which has been involved in airborne radar mapping since the mid-1970s, recognized the commercial benefits of interferometric radar to generate Digital Elevation Models (DEMs) and thus topographic map products, as well as fully Orthorectified Radar Images (ORIs). Since acquiring the technology in 1997, Intermap has been responsible for producing 1 million square kilometres of IFSAR generated DEMs and ORRIs.
IFSAR Technology
The interferometric technology is based on utilizing two radar antennae displaced by a known distance. This antenna separation is referred to as the interferometric baseline. One antenna acts as both a transmitter and receiver; the second as a receiver only. The baseline provides a slightly different path length in the reflection of the radar pulses from terrain points back to the antennae. This path length difference, or phase difference, coupled with precise aircraft positional data, provides the information required to measure the terrain elevation points
IFSAR for topographic mapping uses two apertures separated by a "baseline" to image the surface. The phase difference between the apertures for each image point, along with the range and knowledge of the baseline, is used to infer the precise topographic height of the terrain being image. Intermap’s IFSAR system, is a 3cm wavelength, X-band interferometer operating on Learjet commercial aircraft. Typical data acquisitions are for areas of 10 km across-track (range direction) and 50-200 km along track (azimuth direction), collected at a coverage rate of up to 100km2 every minute. The output of high precision IFSAR datasets is accomplished by on-board laser-based inertia measurement data navigational and differential global positioning system (DGPS) processing to determine the precise position of the Learjet. This IFSAR system was recently modified to increase DEM relative performance, achieving up to 50 cm vertical RMSE, and to increase the orthorectified radar image pixel resolution to 1.25 meter from 2.5 meter. The STAR-3i system is capable of collecting +/- 1-metre vertical data from a flight altitude of 30,000 feet and +/-50-cm from a flight altitude of 20,000 feet. The image resolution remains constant, regardless of the flying altitude and has a positional accuracy of better then 3m.
Figure 2: Learjet and Aero Commander equipped with IFSAR mapping technology
IFSAR based DEMs directly support three very valuable applications:
Intermap has a standard suite of data products and vertical resolutions available. The three core products are: a digital surface model (DSM), a bare-earth digital terrain model (DTM) and an orthorectified radar image (ORI). These three ‘native’ products provide the basic data layers for GIS and imagery applications.
The ORI, or radar image, provides an image of the ground, with a 1.25-meter pixel size (Figure 4). This product resembles an orthorectified, black and white aerial photograph. The key feature of this product is that it provides a means of viewing the earth’s surface in a way that accentuates features far more than is possible with aerial photography. The radar looks to the side of the aircraft and casts ‘shadows’ that enable the user to visually perceive the features in the image – even if they are unfamiliar with the underlying technology. The ORI has many applications in value-added products; it can be used to extract cultural features such as road networks and buildings, it is frequently used in terrain, land cover, environmental and geological analysis and is used in many applications as a seamless base layer for mapping control and quality assurance.
Radar systems collect data from the first surface with which they interact, meaning that the elevation models created from these data represent the elevation of that surface (trees, buildings, towers, etc.). The resulting Digital Surface Models (DSMs) Figure 5, are useful for some applications (e.g., tower siting, viewshed analysis). Many users require elevation data for the bare earth or digital terrain model (DTM) Figure 6. Intermap developed a method of “removing” objects from the terrain surface while retaining the detail in that surface (Wang 2001). This hierarchical surface-fitting method (TerrainFit®) is fully automated and runs on a desktop PC. In standard production mode, ‘false stereo’ image pairs are created from the corresponding orthorectified radar images (ORIs) and are taken, together with the TerrainFit ground points, into a stereo editing environment, where additional quality control and editing activities take place manually. These technology advances now provide a much improved series of radar products - comparable to and complementary with aerial photography and LIDAR -- and the mapping market now has available a broader selection of sensors, capabilities and costs.
Generating 'Real' Maps
The operational approach for using IFSAR data to generate topographic maps is comparable to conventional mapping processes. The IFSAR data is used within a softcopy photogrammetric workstation using traditional photogrammetric methodologies. The stereomate functionality and pseudo-stereo capability permits trained photogrammetric operators to extract topographic features from the IFSAR data. Intermap has been successfully generating 1:10,000-1:50,000 Topographic Maps from the IFSAR data. Road center-line accuracies of better than 3m have been achieved. Given that the IFSAR data processor is semi-automated to output both DEMs and ortho-images in near real-time with little operator interaction, its use results in significant savings in time and labor over traditional photographic mapping techniques.
Figure 7: Process flow for creating topographic maps from IFSAR data using conventional mapping workstations.
The "New National Map" NEXTMap Britain
Intermap’s NEXTMap Britain programme began with a pilot project undertaken in 1998/99. Willis Consulting, a flood risk consultant to the insurance industry, hired Intermap to acquire elevation data in the River Thames drainage basin for use in a new flood risk analysis system. The STAR-3i system was used to collect approximately 22,000 km² of DEM and image data in support of the project. Intermap’s ability to use IFSAR for collection of a wide area in a short time at an affordable price made the project an unqualified success. Subsequently, every insurer with commercial or residential property portfolios in the Thames basin made use of the risk analysis system. In 2001, the insurance industry, led by Norwich Union Insurance, approached Intermap about flying all of the rivers and coastal areas in the country, as they were dissatisfied with the inconsistent data coverages and accuracies available from traditional data sources.
Britain was divided into seven rectangular blocks for the purpose of data acquisition. A total of 221 flight lines are planned, comprising 40,077 line kilometres of acquisition. A total of 56 radar reflectors were precisely positioned throughout the project area to act as ground control for the data sets. To support the positional accuracy of the aircraft, a total of 35 GPS base stations are employed.
Most of the acquisition was flown at 28,000 feet to provide a nine-kilometre swath with a 1.5-kilometre overlap in flight lines. The resulting vertical accuracy for the elevation data is +/- 1.0-metres RMSE. Lowering the flying altitude to 20,000 feet for the southeast of England allowed the capture of approximately 50,000 km² of elevation data with a vertical accuracy of 50-cm RMSE. Both data sets have a DEM posting of 5.0 metres. The ORI resolution is a consistent 1.25 metres and horizontally correct to 3m.. The elevation data and the ORI are fully georeferenced to each other, allowing the ORI to be draped over the DEM to support analysis in a 3-D environment.
Conclusions
IFSAR technology provides a very cost effective solution to national mapping programs. Day/night and most weather and cloud conditions capability means significant cost reductions in data acquisitions. Country-wide coverage in a minimal amount of time provides consistency of data. Minimal control requirements mean reduced costs. “Guaranteed” data acquisition means better allocation of staff resources. Mapping using conventional mapping workstations allows present staff utilization with minimal retraining. Standard IFSAR products allows for consistency in map products. IFSAR technology brings new look to national mapping programs.
References
Garth Lawrence and Marc Wride
Intermap Technologies
400 Inverness Parkway Suite 330
Englewood Colorado
303 708 0955
glawrence@intermaptechnologies.com
mwride@intermaptechnologies.com
Abstract
It has been many years since governments have undertaken national mapping programs with new, up-to-date source materials. Most national programs are limited to reworking existing data or up-dating only a small fraction of the national dataset each year. As a consequence, most national maps are out of date. As well, because of the cost to produce new, more detailed contour data, contour detail and/or accuracy is insufficient for today’s needs.
This paper describes new national mapping programs undertaken with private sector funding and using interferometric synthetic aperture radar (IFSAR) technology to provide highly accurate yet cost effective data. These are called NEXTMap programs. IFSAR technology with its ability to map at night and through clouds reduces time and costs while providing significantly improved accuracy. IFSAR technology provides an economical means of revising and maintaining a country’s topographic database. The combinations of low cost and high performance will not only meet governmental mapping needs but also promises to have significant impact on civil and commercial users. An operational methodology that successfully makes, accurate map products for the commercial and public market sectors is described.
NEXTMap Britain, Jamaica, Puerto Rico and Indonesia represent nation wide mapping programs where new source data is provided by proven IFSAR technology. Intermap Technologies used its proprietary IFSAR systems to provide detailed mapping data for each of these countries. The technology provides imagery with 1.25m pixel size and 3m horizontal accuracy. A digital surface model is collected with the image. The DSM has data points every 5m that are accurate to 3m horizontally and 1m (3m option) vertically. TerrainFitÒ, software designed to remove the effects of trees and buildings, provides a digital terrain model (DTM) of the ground surface.
With today’s cut backs in government funding, NEXTMap programs can be lead by private industry and be available to governments at reduced costs. This paper describes the NEXTMap national mapping programs and the products created from the data.
Introduction
The geographic mapping industry has widely acknowledged that the accuracy and timeliness of national maps have traditionally been poor. Even more troublesome is that the high current cost of data acquisition is restricting efforts by government agencies to effectively update this critical national resource. Existing out-of-date and inaccurate base maps are impacting the utility of national map data in not only traditional mapping applications, but also emerging applications including air and ground navigation systems, 3D visualization products and in orthorectification of airborne and satellite imagery. The high costs of traditional mapping techniques are restricting efforts of local and national governments in updating these maps on a nationwide level. The introduction of a nationwide geospatial data set including a seamless image layer with a resolution of 1.25 meters, and a seamless DEM with a posting of 5 meters, would permanently change the industry landscape.
Traditional photogrammetric mapping technologies are being challenged by high resolution Interferometric Synthetic Aperture Radar (IFSAR) systems. The first rigorous assessment of IFSAR for topography mapping was demonstrated in 1963. Ten years later, the IFSAR technology has advanced to the point where airborne systems are capable of accuracies in the centimeters. The flexibility of IFSAR system deployment (day or night operation), near weather-independent data collection, cloud penetrating capability, and quick turn-around time is providing an alternative to the conventional photogrammetric technology.
Intermap Technologies is the world’s leading IFSAR (Interferometric Synthetic Aperture Radar) remote sensing imagery and elevation data products, company and a leader in the generation of cartographic and other mapping products. Using its IFSAR technology, Intermap has conducted national mapping programs under its NEXTMap banner for Britain, Indonesia, Jamaica, Vanuatu, The Solomon Islands and Puerto Rico
Figure 1: IFSAR derived DEM for the cloud covered country of Jamaica.
The Need for Improvement
The need for improved remote sensing technologies that can quickly determine accurate terrain elevations over large areas evolved from military requirements. Operational requirements dictate the need for an all (reasonable) weather, day/night, high-speed collection and processing capability. To address these needs, the United States Defense Advanced Research Projects Agency (DARPA) initiated a program in 1993 to develop operational airborne IFSAR capability. Intermap acquired this technology in 1997
In response to DARPA’s mandate to ensure commercial utilization of the technology, Intermap invested several millions of dollars in the IFSAR technology. Intermap, which has been involved in airborne radar mapping since the mid-1970s, recognized the commercial benefits of interferometric radar to generate Digital Elevation Models (DEMs) and thus topographic map products, as well as fully Orthorectified Radar Images (ORIs). Since acquiring the technology in 1997, Intermap has been responsible for producing 1 million square kilometres of IFSAR generated DEMs and ORRIs.
IFSAR Technology
The interferometric technology is based on utilizing two radar antennae displaced by a known distance. This antenna separation is referred to as the interferometric baseline. One antenna acts as both a transmitter and receiver; the second as a receiver only. The baseline provides a slightly different path length in the reflection of the radar pulses from terrain points back to the antennae. This path length difference, or phase difference, coupled with precise aircraft positional data, provides the information required to measure the terrain elevation points
IFSAR for topographic mapping uses two apertures separated by a "baseline" to image the surface. The phase difference between the apertures for each image point, along with the range and knowledge of the baseline, is used to infer the precise topographic height of the terrain being image. Intermap’s IFSAR system, is a 3cm wavelength, X-band interferometer operating on Learjet commercial aircraft. Typical data acquisitions are for areas of 10 km across-track (range direction) and 50-200 km along track (azimuth direction), collected at a coverage rate of up to 100km2 every minute. The output of high precision IFSAR datasets is accomplished by on-board laser-based inertia measurement data navigational and differential global positioning system (DGPS) processing to determine the precise position of the Learjet. This IFSAR system was recently modified to increase DEM relative performance, achieving up to 50 cm vertical RMSE, and to increase the orthorectified radar image pixel resolution to 1.25 meter from 2.5 meter. The STAR-3i system is capable of collecting +/- 1-metre vertical data from a flight altitude of 30,000 feet and +/-50-cm from a flight altitude of 20,000 feet. The image resolution remains constant, regardless of the flying altitude and has a positional accuracy of better then 3m.
Figure 2: Learjet and Aero Commander equipped with IFSAR mapping technology
IFSAR based DEMs directly support three very valuable applications:
- Formation of the mapping base layer – allowing all other data layers and images (both aerial and satellite) to be more accurate and "map-ready", particularly in hilly or irregular terrain.
- Add e elevation ("z") data to existing 2D databases and to generate elevation-derived maps (e.g., slope, aspect, runoff).
- Digital "draping" of imagery (or other mapping data layers) over 3D landscapes, allowing users to visualize data that would otherwise be difficult or impossible to interpret.
- High accuracy densely populated digital elevation models (DEMs), including both digital surface (DSM) and digital terrain (DTM) models.
- High-resolution orthorectified radar images (ORIs).
- Ground Control Points (GCPs) - GCPs are readily identified “surveying points” used in imagery orthorectification and the registration of multiple map layers to a common base. They are key to accurate map layer registration.
Intermap has a standard suite of data products and vertical resolutions available. The three core products are: a digital surface model (DSM), a bare-earth digital terrain model (DTM) and an orthorectified radar image (ORI). These three ‘native’ products provide the basic data layers for GIS and imagery applications.
 |  |
| Figure 3: DSM of Wales, United Kingdom | Figure 4: ORI from NEXTMap Britain |
The ORI, or radar image, provides an image of the ground, with a 1.25-meter pixel size (Figure 4). This product resembles an orthorectified, black and white aerial photograph. The key feature of this product is that it provides a means of viewing the earth’s surface in a way that accentuates features far more than is possible with aerial photography. The radar looks to the side of the aircraft and casts ‘shadows’ that enable the user to visually perceive the features in the image – even if they are unfamiliar with the underlying technology. The ORI has many applications in value-added products; it can be used to extract cultural features such as road networks and buildings, it is frequently used in terrain, land cover, environmental and geological analysis and is used in many applications as a seamless base layer for mapping control and quality assurance.
Radar systems collect data from the first surface with which they interact, meaning that the elevation models created from these data represent the elevation of that surface (trees, buildings, towers, etc.). The resulting Digital Surface Models (DSMs) Figure 5, are useful for some applications (e.g., tower siting, viewshed analysis). Many users require elevation data for the bare earth or digital terrain model (DTM) Figure 6. Intermap developed a method of “removing” objects from the terrain surface while retaining the detail in that surface (Wang 2001). This hierarchical surface-fitting method (TerrainFit®) is fully automated and runs on a desktop PC. In standard production mode, ‘false stereo’ image pairs are created from the corresponding orthorectified radar images (ORIs) and are taken, together with the TerrainFit ground points, into a stereo editing environment, where additional quality control and editing activities take place manually. These technology advances now provide a much improved series of radar products - comparable to and complementary with aerial photography and LIDAR -- and the mapping market now has available a broader selection of sensors, capabilities and costs.
 |  |
| Figure 5: DSM from NEXTMap Britain | Figure 6: DTM from NEXTMap Britain |
Generating 'Real' Maps
The operational approach for using IFSAR data to generate topographic maps is comparable to conventional mapping processes. The IFSAR data is used within a softcopy photogrammetric workstation using traditional photogrammetric methodologies. The stereomate functionality and pseudo-stereo capability permits trained photogrammetric operators to extract topographic features from the IFSAR data. Intermap has been successfully generating 1:10,000-1:50,000 Topographic Maps from the IFSAR data. Road center-line accuracies of better than 3m have been achieved. Given that the IFSAR data processor is semi-automated to output both DEMs and ortho-images in near real-time with little operator interaction, its use results in significant savings in time and labor over traditional photographic mapping techniques.
Figure 7: Process flow for creating topographic maps from IFSAR data using conventional mapping workstations.
The "New National Map" NEXTMap Britain
Intermap’s NEXTMap Britain programme began with a pilot project undertaken in 1998/99. Willis Consulting, a flood risk consultant to the insurance industry, hired Intermap to acquire elevation data in the River Thames drainage basin for use in a new flood risk analysis system. The STAR-3i system was used to collect approximately 22,000 km² of DEM and image data in support of the project. Intermap’s ability to use IFSAR for collection of a wide area in a short time at an affordable price made the project an unqualified success. Subsequently, every insurer with commercial or residential property portfolios in the Thames basin made use of the risk analysis system. In 2001, the insurance industry, led by Norwich Union Insurance, approached Intermap about flying all of the rivers and coastal areas in the country, as they were dissatisfied with the inconsistent data coverages and accuracies available from traditional data sources.
Britain was divided into seven rectangular blocks for the purpose of data acquisition. A total of 221 flight lines are planned, comprising 40,077 line kilometres of acquisition. A total of 56 radar reflectors were precisely positioned throughout the project area to act as ground control for the data sets. To support the positional accuracy of the aircraft, a total of 35 GPS base stations are employed.
Most of the acquisition was flown at 28,000 feet to provide a nine-kilometre swath with a 1.5-kilometre overlap in flight lines. The resulting vertical accuracy for the elevation data is +/- 1.0-metres RMSE. Lowering the flying altitude to 20,000 feet for the southeast of England allowed the capture of approximately 50,000 km² of elevation data with a vertical accuracy of 50-cm RMSE. Both data sets have a DEM posting of 5.0 metres. The ORI resolution is a consistent 1.25 metres and horizontally correct to 3m.. The elevation data and the ORI are fully georeferenced to each other, allowing the ORI to be draped over the DEM to support analysis in a 3-D environment.
Conclusions
IFSAR technology provides a very cost effective solution to national mapping programs. Day/night and most weather and cloud conditions capability means significant cost reductions in data acquisitions. Country-wide coverage in a minimal amount of time provides consistency of data. Minimal control requirements mean reduced costs. “Guaranteed” data acquisition means better allocation of staff resources. Mapping using conventional mapping workstations allows present staff utilization with minimal retraining. Standard IFSAR products allows for consistency in map products. IFSAR technology brings new look to national mapping programs.
References
- J. Damron and D. Carlton, "Evaluating IFSAR and LIDAR Technologies Using ArcInfo: Red River Pilot Study." US Army Topographical Engineering Center, 2000.
- Coleman, Diane. 2001. Radar revolution: Revealing the bare earth. EOM, November 2001. 30-33;
- Wang, Yandong, Bryan Mercer, Vincent Tao, Jayanti Sharma and Scott Crawford. 2001. Automatic generation of bare earth digital elevation models from digital surface models created using airborne IFSAR. Proceedings of ASPRS 2001, St. Louis, MO.