{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,2]],"date-time":"2026-04-02T13:57:57Z","timestamp":1775138277359,"version":"3.50.1"},"reference-count":43,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2018,9,25]],"date-time":"2018-09-25T00:00:00Z","timestamp":1537833600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004955","name":"\u00d6sterreichische Forschungsf\u00f6rderungsgesellschaft","doi-asserted-by":"publisher","award":["859774"],"award-info":[{"award-number":["859774"]}],"id":[{"id":"10.13039\/501100004955","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>This work focuses on the accuracy estimation of canopy height models (CHMs) derived from image matching of Pl\u00e9iades stereo imagery over forested mountain areas. To determine the height above ground and hence canopy height in forest areas, we use normalised digital surface models (nDSMs), computed as the differences between external high-resolution digital terrain models (DTMs) and digital surface models (DSMs) from Pl\u00e9iades image matching. With the overall goal of testing the operational feasibility of Pl\u00e9iades images for forest monitoring over mountain areas, two questions guide this work whose answers can help in identifying the optimal acquisition planning to derive CHMs. Specifically, we want to assess (1) the benefit of using tri-stereo images instead of stereo pairs, and (2) the impact of different viewing angles and topography. To answer the first question, we acquired new Pl\u00e9iades data over a study site in Canton Ticino (Switzerland), and we compare the accuracies of CHMs from Pl\u00e9iades tri-stereo and from each stereo pair combination. We perform the investigation on different viewing angles over a study area near Ljubljana (Slovenia), where three stereo pairs were acquired at one-day offsets. We focus the analyses on open stable and on tree covered areas. To evaluate the accuracy of Pl\u00e9iades CHMs, we use CHMs from aerial image matching and airborne laser scanning as reference for the Ticino and Ljubljana study areas, respectively. For the two study areas, the statistics of the nDSMs in stable areas show median values close to the expected value of zero. The smallest standard deviation based on the median of absolute differences (\u03c3MAD) was 0.80 m for the forward-backward image pair in Ticino and 0.29 m in Ljubljana for the stereo images with the smallest absolute across-track angle (\u22125.3\u00b0). The differences between the highest accuracy Pl\u00e9iades CHMs and their reference CHMs show a median of 0.02 m in Ticino with a \u03c3MAD of 1.90 m and in Ljubljana a median of 0.32 m with a \u03c3MAD of 3.79 m. The discrepancies between these results are most likely attributed to differences in forest structure, particularly tree height, density, and forest gaps. Furthermore, it should be taken into account that temporal vegetational changes between the Pl\u00e9iades and reference data acquisitions introduce additional, spurious CHM differences. Overall, for narrow forward\u2013backward angle of convergence (12\u00b0) and based on the used software and workflow to generate the nDSMs from Pl\u00e9iades images, the results show that the differences between tri-stereo and stereo matching are rather small in terms of accuracy and completeness of the CHM\/nDSMs. Therefore, a small angle of convergence does not constitute a major limiting factor. More relevant is the impact of a large across-track angle (19\u00b0), which considerably reduces the quality of Pl\u00e9iades CHMs\/nDSMs.<\/jats:p>","DOI":"10.3390\/rs10101542","type":"journal-article","created":{"date-parts":[[2018,9,25]],"date-time":"2018-09-25T11:12:26Z","timestamp":1537873946000},"page":"1542","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Impact of the Acquisition Geometry of Very High-Resolution Pl\u00e9iades Imagery on the Accuracy of Canopy Height Models over Forested Alpine Regions"],"prefix":"10.3390","volume":"10","author":[{"given":"Livia","family":"Piermattei","sequence":"first","affiliation":[{"name":"Department of Geodesy and Geoinformation, TU Wien, 1040 Wien Austria"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0943-2454","authenticated-orcid":false,"given":"Mauro","family":"Marty","sequence":"additional","affiliation":[{"name":"Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, 8903 Birmensdorf, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7572-7701","authenticated-orcid":false,"given":"Wilfried","family":"Karel","sequence":"additional","affiliation":[{"name":"Department of Geodesy and Geoinformation, TU Wien, 1040 Wien Austria"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3716-8961","authenticated-orcid":false,"given":"Camillo","family":"Ressl","sequence":"additional","affiliation":[{"name":"Department of Geodesy and Geoinformation, TU Wien, 1040 Wien Austria"}]},{"given":"Markus","family":"Hollaus","sequence":"additional","affiliation":[{"name":"Department of Geodesy and Geoinformation, TU Wien, 1040 Wien Austria"}]},{"given":"Christian","family":"Ginzler","sequence":"additional","affiliation":[{"name":"Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, 8903 Birmensdorf, Switzerland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2348-7929","authenticated-orcid":false,"given":"Norbert","family":"Pfeifer","sequence":"additional","affiliation":[{"name":"Department of Geodesy and Geoinformation, TU Wien, 1040 Wien Austria"}]}],"member":"1968","published-online":{"date-parts":[[2018,9,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"232","DOI":"10.1016\/j.foreco.2015.10.018","article-title":"Use of WorldView-2 stereo imagery and National Forest Inventory data for wall-to-wall mapping of growing stock","volume":"359","author":"Immitzer","year":"2016","journal-title":"For. 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