Some Notes on Using Balloon Photography For Modeling the Landslide Area

Transcription

1 Some Notes on Using Balloon Photography For Modeling the Landslide Area Catur Aries Rokhmana Department of Geodetic-Geomatics Engineering Gadjah Mada University Grafika No.2 Yogyakarta Indonesia caris@ugm.ac.id Abstract In General, the landslide area in Indonesia has specific characteristic such as small area (less than 100Ha), vegetation coverage, and extreme topography. There are others non-technical problems also such as budget limitation and human resources. The challenges is to develop the appropriate system for modeling the landslide area that characterized by low-cost, easy in operation, fast in production, and good quality. Some experience has been done by using the balloon photography as the main acquisition system. This paper shows some notes on using the balloon photography system for modeling the landslide area. It is including the system architecture, the field procedures, the processing enhancement, and some limitations. Some examples show to explain some problems that caused by vegetation covered and the extreme topography. In some case area, the balloon photography can be a good choice to modeling the surface of the earth. Keywords: balloon photography, digital photogrammetry, landslide area 1. Introduction Today in Indonesia, there are some hazardous landslide areas that have not been mapped in good scale for the geotechnical analysis. In general, the landslide area have some specific characteristics such as (1) the main object area has less than 100Ha; (2) located in extreme and varies topography; and (3) covered by small vegetation. There are having non-technical aspects also, which are (1) lack of budget; and (2) human resources problems in the local area. The modeling landslide area is one of the activities in monitoring and volumetric calculation. The 3D model is used for precise object measurement, location selecting for others sensor, and good illustration for the local community. So, the precise modeling can be one of the supplement system beside the tilt meter or extensometer system. The precise 3D model is used for the geotechnical analysis. In general, the terrain model should have accuracy up to decimeter level. Further, the need for geo-location accuracy is less than the dimension accuracy (3D model). According to the lack of budget, it is need to develop the measuring system that characterized by cost-effective, fast in production, easy to operate, and appropriate accuracy. This paper shows the using of balloon photography system to answer the problem. The balloon system design should has characteristics such as (1) good GSD (Ground Spatial Distance) less than 10cm; (2)portable and easy in operation; (3) produce stereo viewing; and (4) good accuracy in decimeter level. 1

2 2. The Balloon Photography System The motivation of using the balloon system is because it is lower cost (< 400 $US). The balloon platform is the same as the outdoor advertising balloon. Other reason is because the topography and the vegetation covered make difficulty for takeoff-landing maneuver. Some of the past researchers (see Seang, et.al. (2006); Altan, et. Al. (2007)) have used the balloon system (see Figure 1) Figure1. Illustration of System Architecture (Seang, et.al. 2006) The balloon platform is the spherical balloon with 2.5m in diameter that it has hydrogen gas volume up to 8 m.cu. The platform uplift is up to 8 kg that including the 5kg of the balloon weight. The digital camera Nikon P50 (wide angle) with 8 MP is used for imaging sensor. The life view camera is transmitting to the cameraman with video sender system. The range capability of the video sender is up to 1km. The 2-axis camera mounting system is used to control the tilt and yaw movement remotely. The 4 channel remote-control (Futaba 4ex series) is used to control 3 electric servos remotely up to 1km range distance. The 2 servos are used for moving the 2-axis mounting system, and 1 servo is used for shutter button. The exposure has done by looking at the pocket TV monitor, so it can take the picture at the right angle viewing. The ground system is including (1) pocket TV for viewing life view from video sender; (2) R/C transmitter; (3) nylon rope; (4) battery 12V, and (5) Delorme Earthmate Blue Logger GPS receiver. Figure 2 shows some of the ground instrument 2

3 Figure 2. Ground instrument The flight planning and the geometry exposure position are difference with the conventional aerial platform; these are due to some reasons, such as: 1. The balloon platform did not have maneuver just like airplane or Helicopter. The flying high can be varies, it is controlled by the rope length and wind speed. In general with medium wind speed (30km/h), the balloon position can be varies up to 15m at rope length 150m. 2. The terrain slope condition is rather extreme up to 45 degree (see Figure 4). 3. The area is less than < 100Ha. 4. The terrain model accuracy is more important than geo-position component So, the best exposure configuration is to use the oblique aerial photograph. In 300m rope length, the coverage area from the nadir view angle up to 7-8 Ha. Furthermore, the spacing distance between exposures is up to 400m. In every exposure position, the nine viewing exposures angle are taken, which are: 1 nadir view, and 8 oblique views. Figure 3 shows the illustration for camera viewing position. 3. Some Problems And Solutions Figure 3. The camera viewing exposure 3

4 The processing system is same as the digital photogrammetry system workflow. Firstly, the block photo geometry is processed to produce 3D model coordinates with bundle adjustment. The model should be scaling to get the right object dimension. The three length measurements are used for scaling the model. Furthermore, the following notes should be taken care in using balloon system: 1. The calibration camera should be implemented to get the right intrinsic/interior parameter. The choice of using Nikon P50 (wide angle) can increase the lens distortion factor. The experience of using Nikon P50 shows the precision can be improved up to 9 times by applying the calibration parameter. 2. The existing of vegetation cover can be problem to see the terrain, especially in the breakline area. This problem can be reduced by adding some breakline and interpolation calculation. 3. Flying with the balloon platform is optimum at wind speed less than 10km/jam. In mountain area (landslide area), the wind speed condition can be accepted in the morning before 10am. So, the optimum operational time is limit. The tetrad or zeppelin balloon shape can handle wind speed more stable than spherical shape. 4. In Terrain model production, which is using the oblique photo, the stereo plotting with automatic matching technique is difficult. So, the best choice is to use the tie-point or pass point directly as a spot high. 5. Some Results The basic products of the balloon photography are the aerial photo in nadir or oblique view (see figure 4). This can be use for some applications such as property/developer, surveillance, agriculture, etc. Figure 4. Example single exposure in nadir and oblique view from 280m high. The final product for landslide study is the digital terrain model that precisely represent the terrain condition, including the vegetation coverage and some others sensor picture. For the 4

5 mapping product, it can produce contouring map and orthophoto map. Figure 5 show some result that can compared with the oblique at figure Conclusion Figure 5. Visualization some results products This paper illustrates the using of balloon photography system for modeling the landslide area up to 100Ha. Some good characteristics of the system have shown which are using the electronic / hobby consumer s instrument. There are some notes should be implemented to improve the accuracy ability. The final product of this system is terrain model that can be used to generate 3D visualization, volumetric calculation, and mapping product. Reference Seang, T.P. And Jan-Peter MUND, 2006, Balloon Based Geo-Referenced Digital Photo Technique a Low Cost High-Resolution Option for Developing Countries, XXIII FIG Congress, Munich, Germany, October 8-13, 2006 Altan, M.O, T. M. Celikoyan, G. Kemper, G. Toz, 2005, Balloon Photogrammetry For Cultural Heritage, SS 4: CIPA Low-Cost Systems in Recording and Managing the Cultural Heritage. 5