Leica Geosystems Geospatial Imaging
The ADS40 Airborne Digital Sensor is currently the only commercial sensor capable of acquiring colour and false colour strip images in the low decimeter range at the same high resolution as the black and white stereo images. This paper delves into the technicalities of ADS40 and the role of high resolution colour imagery for orthomaps and remote sensing
Introduced in 2001, the Leica ADS40 was the first digital airborne sensor delivered commercially to the photogrammetric community. The primary guiding principle in the design of this sensor was to create an airborne imaging system which was not hampered by limitations known to the established photogrammetric community. The new design allows for an optimal adaptation to the needs of the digital workflow. The ADS40 Airborne Digital Sensor is currently the only commercial sensor capable of acquiring color and false color strip images in the low decimeter range at the same high resolution as the black and white stereo images. The high resolution of 12,000 pixels across the entire swath and 100% forward overlap in the image strips allow a variety of mapping applications to benefit from this sensor.
Although digital data processing opens the opportunity to implement computational methods to convert central perspective projection into an orthogonal projection, the line sensor’s parallel perspective geometry offers a unique opportunity to produce images, which in the flight direction can be considered quasi-orthogonal projections. Line sensor data is as close to a map’s orthogonal projection as is technically possible.
The nadir line CCD produces an image strip also called pixel carpet. This quasi-orthogonal image is as close to a perfect orthogonal image of the earth’s surface as any image made through a single lens will ever get.
It is this close relationship between the nadir image captured from a push-broom sensor and a truly orthogonal projection which makes the ADS40 images attractive for further processing. The production of true orthophotos requires the determination of a Digital Surface Model (DSM) from all three panchromatic stereo images. Apart from this, the line sensor’s 100% overlap of stereo strip imagery has other benefits:
- Minimal data for least occlusions in true-ortho maps
- Height/base ratio
- Forward Motion Compensation is inherent in the image acquisition principle
- Nadir image strip only uses the best part of the field of view
- Streamlined mosaiking of image strips
- Excellent tool for BRDF