GEO-REFERENCED AERIAL BALLOON PHOTO TECHNIQUE

Low cost high-resolution option for developing countriesTeng Peang Seng (PGEC) & Jan-Peter Mund (CIM)

Dr. Jan-Peter Mund (PhD Geographer)Tel. ++855-(0)12-333537, e-mail: jpmun03@yahoo.comGerman Technical Cooperation (gtz), Phnom Penh

Royal University of Agriculture (RUA) Faculty of Land Management and Land Administrationwww.rua.edu.kh/land_mgt.html

Mr. Teng Peang Seng (PGEC-Manager)Tel. ++855-(0)12-880878e-mail: 012880878@mobitel.com.kh

A Collaboration of the Geomatics Education Center and theGerman Technical Cooperation to the KINGDOM of CAMBODIA:

Phnom Penh Geomatics Education Centre (PGEC) Centre for International Migration (CIM)

German Technical Cooperation (gtz)

Abstract

The paper introduces and assesses the highly efficient amateur aerial balloon photo technique, which makes aerial photos affordable at a price of 0.10 – 0.35 US cents per hectare. The idea was to provide an inexpensive but quality efficient solution for recent aerial color photos on a high pixel resolution while orthophotos are not everywhere accessible in Cambodia. Other high resolution images from advanced scanners like Quickbird, Ikonos or others are most likely unaffordable due to insufficient decentralized budget in Cambodia. As a consequence topographical and other spatial data are more or less missing in planning offices and enhancement and modifications basically are not easy to integrate into smaller scaled planning resources. This modern technique is based on a simple plastic balloon (r=3m), inflated with hydrogen gas, chemically produced on the site and adapted to the conditions in developing countries especially for areas with rapid land use changes. In Cambodia it is presented by a private geo-spatial company, the Phnom Penh GeoinformaticsEducation Centre (PGEC) in collaboration with the Faculty of Land Management and Land Administration at the Royal University of Agriculture.

The rectified, merged and geo-referenced aerial balloon-photos with surface resolution per pixel vary among 20m to 0.4m, depending on altitude of the platform and camera capacity, are enlargeable up to a scale of 1:1.000 without any loss in optical and spatial quality. Methodologically the approach uses typical image processing, enhancement and geo-referencing techniques like haze elimination, merging and mosaic procedures, mostly provided by ERDAS IMAGINE software. The aerial photo collection follows standard aerial photo measures like flight line preparation, synchronization of camera and GPS clocks as well as ground truth samples.

The balloon based digital aerial photos from a non calibrated digital camera (Olympus C-70) are already integrated in decentralized regional and urban planning processes in Cambodia as well as geospatial education, data trainings. Further outcomes of this technique are lately renewable detailed land use maps as well as other planning sources for real estate validation and environmental protection strategies i.e. buffer zoning concepts. Besides, they are expected to be useful for other “small area” projects like village based land use planning, technical implementations or (eco-) tourism projects at specific locations and retakes of the same photos within a high-level time resolution of one or two years.

4. Mapping ScalesMaps = 1:1000 – 1:10.000

Scale per pixel depending on distance: 20 cm up to 2 m

Precision of reference technique:Spot- Image -> 2-3 Pixel (< 80cm)

Topographic Maps 1:100.000 (< 200cm)Handheld GPS (8-15 m inaccuracy ) (5-10 m)

Differential Post processing GPS (1-2 m)

in Cooperation with: MLMUPC; Phase 2

1. The Challenge:• Simple technical solution, available in Cambodia• Digital Camera: Olympus CAMEDIA C70 7..2

Megapixel• Infrared timer • 4 Handheld GPS Garmin 76CSMap• Inflatable balloon made of thin, strong PE fabric• Fixed with 8 thin, easy to control• Flexible and uncomplicated for transportation

3. Remote sensing methods used:• Wind speed measurement• Camera calibration• Continuous picture acquisition

up to 2h• Digital data transfer • Atmosphere correction• Image enhancement • Cloud mask cover reduction• Image addition and merging • Geo-correction with GPS and SPOT• Geo-reference correction

with Aerial Photos • Time series analyses: • Orthoimage 2001; 2004; 2006

Standardized low cost application• 200 $ per km² with 1-5 pictures• 150 $ per km² > 5 pictures

2. Technical Balloon Application

Balloon gas = Hydrogen

Local production at the site: Aluminum cans +Natriumhydroxide + Water

(AL+NaOH+3H2O= Na[AL(OH)4]+1,5H2O)=> Hydrogen + Natriumaluminat

5. Geodetic -cartographic difficultiesNo precise geodetic, or topographic network available yetOnly five trigonometric reference points (1st order) existing Localization of Nadir-points with post processing GPSTwo different UTM projections applied in CambodiaThree datum parameters applied: Indian 54, Indian 60, WGS84