Printer friendly format

Page 1 of 3
| Next |


Characteristics of New Generation of Digital Aerial Cameras

John Trinder
John Trinder
School of Surveying and SIS
University of NSW
UNSW SYDNEY 2052 NSW
AUSTRALIA
Email: j.trinder@unsw.edu.au


ABSTRACT
There has been considerable debate recently on the future of film and digital images in photogrammetry. While film images will still be acquired by some organization in the near future, the issue is more likely when, rather than if will the digital technology lead to the demise of the small but currently essential aerial film industry. Given the apparent advantages of digital over film aerial images and the expected reduction in cost of digital cameras in the future, there is a growing acceptance of digital camera technology for aerial photography. This paper will describe some of the characteristics of the new generation of cameras, their advantages and some operational aspects.

THE DEVELOPMENT OF DIGITAL CAMERAS
The development of digital aerial cameras has advanced significantly over the past 4-5 years, and worldwide sales are reportedly growing rapidly with a number of companies entering the market. Modern aerial film cameras have reached a high level of development, with very high spatial resolution, geometric quality, wide angle of coverage, and overall efficiency for map production. Film image is also a very efficient medium for long-term storage of spatial information describing the terrain surface. In order for digital aerial cameras to compete with film aerial cameras they need to be able to acquire high resolution images with similar or better accuracies, have comparable angles of field, be suitable for mapping and orthophoto production, and take advantage of the particular characteristics of digital image acquisition. While the majority of these aims have been largely achieved, the solution to the issue of long-term storage of digital information is still open.

The two approaches to the design of digital aerial cameras are:
  • Systems based on linear array scanners (pushbroom). Linear array scanners acquire data by scanning the terrain with one or more linear arrays as the aircraft moves over the terrain, in much the same way as a broom sweeps a surface. They normally incorporate at least three sensors, one looking forward, one looking vertically and one backwards to acquire three separate overlapping images of the terrain that can be used for determining elevations. Multispectral images at the same or reduced resolution may also be acquired. An integrated GPS/IMU system is essential for this configuration for the determination of camera position and tilts, because the image acquisition is a continuous process and not frame based.
  • Systems based on area arrays. These systems may involve single area arrays (usually referred to as medium resolution) or multiple arrays whose images are stitched together to form a larger frame image (referred to as high resolution). The formats of the images may not be square, but their dimensions approach those of frame aerial film cameras. These frame images can be processed using standard digital photogrammetric software. GPS/IMU system will not be essential for its operation, but some components of such a system may be included as an option.
The general characteristics of most of these digital cameras are:
  • 12 bit dynamic range of panchromatic images with ground pixel sizes as small as 5cm
  • Most acquire multi-spectral images, some with larger pixel sizes than for the panchromatic images, covering wavelengths from blue to NIR
  • High geometric accuracies
  • Data storage requirements total many TerraBytes both for the original data and backup
Page 1 of 3
| Next |