Abstract
Abstract. Since manned, airborne aerial reconnaissance for archaeological purposes is often characterised by more-or-less random photographing of archaeological features on the Earth, the exact position and orientation of the camera during image acquisition becomes very important in an effective inventorying and interpretation workflow of these aerial photographs. Although the positioning is generally achieved by simultaneously logging the flight path or directly recording the camera's position with a GNSS receiver, this approach does not allow to record the necessary roll, pitch and yaw angles of the camera. The latter are essential elements for the complete exterior orientation of the camera, which allows – together with the inner orientation of the camera – to accurately define the portion of the Earth recorded in the photograph. This paper proposes a cost-effective, accurate and precise GNSS/IMU solution (image position: 2.5 m and orientation: 2°, both at 1σ) to record all essential exterior orientation parameters for the direct georeferencing of the images. After the introduction of the utilised hardware, this paper presents the developed software that allows recording and estimating these parameters. Furthermore, this direct georeferencing information can be embedded into the image's metadata. Subsequently, the first results of the estimation of the mounting calibration (i.e. the misalignment between the camera and GNSS/IMU coordinate frame) are provided. Furthermore, a comparison with a dedicated commercial photographic GNSS/IMU solution will prove the superiority of the introduced solution. Finally, an outlook on future tests and improvements finalises this article.
Highlights
1.1 Oblique archaeological reconnaissanceTo date, the common practise of archaeological aerial photographic reconnaissance is quite straightforward and seems not to have significantly changed over the past century
Since manned, airborne aerial reconnaissance for archaeological purposes is often characterised by more-or-less random photographing of archaeological features on the Earth, the exact position and orientation of the camera during image acquisition becomes very important in an effective inventorying and interpretation workflow of these aerial photographs
Gobal Navigation Satellite System (GNSS) sensors are nowadays found in many electronic devices and their integration with digital cameras became a common approach
Summary
The common practise of archaeological aerial photographic reconnaissance is quite straightforward and seems not to have significantly changed over the past century. Once an archaeological feature is detected, it is orbited and documented from various positions (generally from an oblique point of view). This type of aerial photographic reconnaissance has been the workhorse of all archaeological remote sensing techniques since it is one of the most costeffective methods for site discovery and the non-invasive approach yields interpretable imagery with abundant spatial detail (Wilson, 2000). Due to the fact that flying paths and photo locations are never predefined in this oblique reconnaissance approach and accurate mapping and photo interpretation necessitates knowledge about the part of the Earth’s surface covered by the aerial image, the latter information should ideally be recorded during photo acquisition. In the worst case scenario, retrieving the exact location of a specific aerial image might even prove impossible
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