Degree: PhD or MSc (by research)

Key-words: Orthorectification, aerotriangulation, airborne video imaging

Entry: BSc(Hons), preferably 1st class, or MSc, in Engineering, Mathematics, Photogrammetry, Geodesy or Physics.

Supervisor(s): Dr Derek Lichti

Project Funding: Industry

Student Funding: Student required to win ASA, IPRS or other scholarship

Resources: Helava digital photogrammetric workstation, digital cameras, camera calibration facilities, GPS hardware

Starting Date: Unrestricted

Airborne digital multi-spectral imaging systems are well-established, low-cost tools for collection of remotely sensed digital imagery for land use management and monitoring applications. Typically, a system consists of four digital cameras rigidly mounted on a platform adjacent to each other. Each camera’s lens is fitted with a different narrow bandpass interference filter that provides high spectral resolution on the order of a few tens of nanometres. Four camera systems are typically fitted with blue, green, red and near infra-red filters. Each camera outputs an image of digital numbers that are proportional to the incident radiance landing on each sensor.

The radiometric information (i.e., digital numbers) from each spectral band are used to derive measures that indicate the type and state of land cover within the monitoring area. Documented applications of airborne digital multi-spectral imaging include monitoring of forest damage due to acidic mine tailings (Lévesque and King, 1999), precision agriculture (Metternicht et al., 2000) and estimation of suspended sediment concentration (Liedtke et al., 1995).

Of paramount importance to the success of an airborne digital image monitoring campaign is the correction of the imagery for distortions or errors, which can be broadly classified as radiometric and geometric. Radiometric errors influence the amount of energy received by the CCD detector and, hence, the digital numbers recorded by the imaging system. Geometric distortions, the focus of this research, are displacements of imaged points from their expected locations and can be attributed to platform tilt at the time of image acquisition, inherent perspective distortion, lens distortion and relief displacement. Correction of these errors (rectification) produces an orthographic projection of the imagery, an orthoimage.

The removal of geometric distortions from airborne digital imagery is typically handled with polynomial models that warp the imagery to fit ground control. As higher resolution cameras are becoming more readily available, residual distortions, due to terrain relief in particular, become more significant. Thus, there is an emerging need to abandon the polynomial rectification approach in favour of rigorous rectification. Moreover, there also is growing interest in exploiting airborne digital imaging for photogrammetric mapping.

The proposed project will involve research into one or more of the following:

1. Geometric system calibration. As with any photogrammetric system, accurate positioning demands rigorous camera calibration. The four-camera configuration of airborne digital imaging systems poses new challenges in terms of interior and relative orientation calibration. This aspect of the project will focus on development of mathematical models and procedures for simultaneous calibration of the interior and relative orientation of multi-spectral imaging systems.

 

2. Aerotriangulation. Prior to rectification, the imagery must be triangulated to estimate the exterior orientation parameters. High parameter correlation arising from the narrow field of view (FOV) of the digital cameras presents the problem of how to best incorporate external sensor information (e.g., GPS observed perspective centres) and geometric system constraints. Additionally, the narrow FOV makes for a small base to height (B/H) ratio, which degrades the accuracy of object point height estimation. This project will examine these issues along with the stochastic modelling of image point observations to account for image blur, SNR and camera spectral sensitivity.

 

3. Orthorectification. This aspect of the research will be an examination of strategies for digital elevation model and orthoimage production from triangulated airborne digital imagery. Specifically, the global object reconstruction method (Heipke, 1992; Holm and Rautakorpi, 1998) will be extended to allow optimal integration of the imagery for all four spectral bands.

Dare, P.M., C.S. Fraser and A.M. Judd (2000) Automatic linear infrastructure mappping using airborne video imagery. Proceedings of the ASPRS Annual Conference, May, Washington DC, On CD.

Edirisinghe, A., G.E. Chapman and J.P. Louis (2001) Radiometric calibrations for multispectral airborne video imagery. Photogrammetric Engineering & Remote Sensing, 67 (8): 915-922.

Fraser, C.S. (1997) Digital camera self-calibration. ISPRS Journal of Photogrammetry & Remote Sensing, 52 (4): 149-159.

Graham, W. and J. P. Mills (2000). Small format digital cameras for aerial survey: where are we now? Photogrammetric Record, 16 (96): 905-909.

Heipke, C. (1992) A global approach for least-squares image matching and surface reconstruction in object space. Photogrammetric Engineering & Remote Sensing, 58 (3): 317-323.

Holm, M. and S. Rautakorpi (1998) Experiences of automatic creation of image mosaics and digital surface models using airborne digital camera data. Videometrics VI, San Jose, CA.

King, B. (1995) Bundle adjustment of constrained stereopairs-mathematical models. Geomatics Research Australasia, 63: 67-92.

King, D. (1992) Evaluation of radiometric quality, statistical characteristics and spatial resolution of multispectral videography. Journal of Imaging Science and Technology, 36 (4): 394-404.

King, D., P. Walsh and F. Cuiuffreda (1994) Airborne digital frame camera imaging for elevation determination. Photogrammetric Engineering & Remote Sensing, 60 (11): 1321-1326.

King, D.J., C. Armenakis and A. Chichagov (1995) The use of airborne digital frame camera imagery for DEM generation. Geomatica, 49 (4): 489-497.

Lévesque, J. and D.J. King (1999) Airborne digital camera image semivariance for evaluation of forest structural damage at an acid mine site. Remote Sensing of Environment, 68 (2): 112-124.

Liedtke, J., A. Roberts and J. Luternauer (1995) Practical remote sensing of suspended sediment concentration. Photogrammetric Engineering & Remote Sensing, 61 (2): 167-175.

Maas, H.-G. and T. Kersten (1997) Aerotriangulation and DEM/orthophoto generation from high-resolution still-video imagery, Photogrammetric Engineering & Remote Sensing, 63 (9): 1079-1084.

Metternicht, G., F. Honey, G. Beeston and S. Gonzalez (2000) Airborne videography for rapid assessment of vegetation conditions in agricultural landscapes. Proceedings of 10th Australasian Remote Sensing and Photogrammetry Conference, Adelaide, SA, August, 412-424.