20^th Annual International Esri User Conference, San Diego, Cal. June 26^th-30^th, 2000

Authors Names:

Energy providers need detailed information about the location and the present technical status of their facilities network. Energy lines often follow rough terrain and therefore permanent monitoring and acquisition of accurate and current data and their management is mandatory.

Esri Germany, TOPOSYS and Rotorflug developed a new technology by integrating airborne laserscanner data into a GIS-based "Powerline Management Information System". The combination of several basic technologies provided by the consortium meets above requirements on accuracy and provides easy access on the database. In more details the system features:

• Digital survey of the terrain structure (incl. vegetation, buildings etc.) by the laserscanner technology of TopoSys (laserscanner data, image data)

• Application of high-end helicopter flight management with helicopters of the company Rotorflug

• Delivery and maintenance of the worldwide leading GIS-Software of the Esri Group to process and integrate geographic and remote sensing data in the computer system of the client

• GIS-Database design, processing and database creation, georeferencing and creation of the Powerline Management Information System by the Planning and Consulting Company Prof. Schaller

The described system solutions are open and compatible. According to clients requirements the provision of pure data, consulting, the software of the Powerline Management Information System or the turnkey complete system (incl. training and maintenance of client’s staff) is available.

The TopoSys laserscanner system is designed to produce digital elevation models (DEMs) of the environment at a typical accuracy of 0.5 m in x, y and 0.15 m in z. The exceptional measurement frequency of 83000 measurements per second results in about five measurements per m˛ on ground, when surveying from an aeroplane – from a helicopter the measurement density is even higher. This measurement density and the regular scan pattern (parallel lines) form the basis for high quality DEMs.

In the recent years an increasing demand on high-precision digital elevation models (DEMs) has to be noted - high-precision in this sense means that the accuracy of the DEMs is better than 1m in x,y and about 0.2m in z. Many of those applications not only request for high precision, but also demand a short delivery time. Typical applications are monitoring of coastal erosions, simulation of floods in river basins in order to determine engineering works, and simulation of emitter sites or line-of-sight calculations for mobile communication networks.

The TopoSys laserscanner system integrated into a fixed wing aircraft has delivered thousands of km˛ of high resolution DEM for such applications. Recently the TopoSys system has been mounted into a helicopter to start a new application: Integrated Helicopter Corridor Mapping.

All the various sensor data (see also Figure 1) are recorded digitally during the laser scanner survey. LINS, GPS, laser data and RGB linescanner data are stored on exchangeable PC harddisks, only video data are stored on a digital tape. During the survey the operator controls the performance of the system, in case of the laser data with help of a real-time waterfall display.

GPS data is registered with help of a Novatel Millennium L1/L2 receiver at a data rate of 1 Hz, while the high precision LINS (Laser Inertial Navigation System) collects position and attitude data at a data rate of 64 Hz. After flight path restitution and merging of dGPS and LINS measurements, position and attitude data are available at 64 Hz.

Fig.1 IHCM System Components

Fig.2 Equipment mounted in a helicopter for on flight operation

The eye-safe laser sensor operates at 1.54 µm, a pulse rate of about 83 kHz and a scan frequency of 630 Hz. The scan angle is fixed to +/- 7° in order to minimise shading effects especially at the borders of the scan. From a survey altitude of 1000 m the swath on ground is about 250 m. Swath width – and measurement density – can be adapted by selecting the appropriate the survey altitude.

The down-looking video camera, which was part of the sensor package up to now, is replaced by a four-channel linescanner (R, G, B, IR). The linescanner provides a pixel size of about 0.4 m from a survey altitude of 1000 m and allows generating "ortho-photos" of the survey area. The line-scanner data are expected to support the identification of vegetation, too.

The application "Integrated Helicopter Corridor Mapping (IHCM)" is done from a helicopter like a Bell Jetranger 206. In case of IHCM, a 45° forward looking digital video camera additionally records a video sequence of the surveyed tracks (see also Figure 3). Typically survey altitudes in IHCM applications are between 200m and 500 m above ground.

Fig.3 IHCM Sensor package in a helicopter

The off-line data processing is done by high-end PCs. Key software packages are a package for flight path restitution and the TopoSys software for DEM generation and post-processing; IHCM post-processing is made by a special package in ARCINFO and ERDAS environment.

The present TopoSys I system will be replaced by the TopoSys II series in late autumn 1999. Performance parameters of TopoSys II are given in the following table.

Table 1. Performance Parameters of TopoSys II

sensor type	pulse modulated laser radar
range	» 1’600 m
scanning principle	fibre optic line scanner
transmitter	solid state at 1.5 µm
measurement principle	run-time measurement, intensity, first + last pulse
laser pulse rate	83’000 Hz
scan frequency	630 Hz
field of view	+/- 7°
number of pixels per scan	127
swath width (at 1’000 m flight height)	250 m
resolution of a distance measurement	< 0.03 m
height accuracy of TopoSys DEMs	< 0.15 m
laserscanner classification	class 1 by EN 60825 (eye-safe)