Abstract
On the seasonal timescale, for accessible locations and when manpower is available, direct observations and field surveys are the most useful and standard approaches. However very limited studies have been conducted through direct examination on decennial-to-century timescales due to observational constrains. Here, we present an open and reproducible pipeline based on historical aerial images (across a timeline of up to 70 years) that includes sensor calibration, dense matching, and elevation reconstruction in two areas of interest that represent pristine examples of tropical and alpine environments. The Remparts and Langevin rivers, on Réunion Island, and the Bossons glacier, in the French Alps, share limited accessibility (in time and space) that can be overcome only by remote sensing. We reach a metric-to-submetric resolution close to the nominal image spatial sampling. This provides elevation time series with better resolution than most recent satellite images, such as Pleiades, in a decennial time period.
Highlights
On the seasonal time scale, for accessible locations and when manpower is available, direct observations and field survey are the most useful and standard approaches
In order to automatically produce time series of digital surface model (DSM), from large volumes of archived images and within the previously identified limits, we propose a complete workflow with new approaches on pre-processing and canvas co-registration steps
We summarize our new approach for the production of time series DSM from archived aerial images: -I- Download the scanned archived aerial images from online catalogs or manually scanned achieved films, of each campaigns of the studies times series -II- Pre-process all the images from all the campaign with FiducilLib in order to transform the scanned images into images taken by digital cameras. -III- Designation of the campaign of reference and selection of the ground control points (GCP) for the campaign of reference
Summary
M OUNTAINOUS landscapes under tropical and alpine environments share a number of characteristics. Once being identified and located in each pictures, these marks are used to re-project and crop the images so that they are mapped as if they had been acquired digitally in the first place For this remapping, an affine transformation is generally considered to overcome potential misalignment due to the manual scanning procedure, relative orientation of the camera that took the pictures under consideration. After computing the relative orientation for every image, another procedure is required in order to accurately place this orientation into a georeferenced coordinate system This is done by retrieving the absolute orientation of the cameras (i.e., inference of R, t, w) using external geographical information, called reference points or Ground Control Point (GCP). Other tests such as the the variation in elevation over areas known to be stable over the decade time scale studied need to be evaluated
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