Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data
In forest management, site index information is essential for planning silvicultural operations and forecasting forest development. Site index is most commonly expressed as the average height of the dominant trees at a certain index age, and can be determined either by photo interpretation, field me...
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doaj-4aefd39bbe1e4fccb25cc9fd160e67e72020-11-25T00:40:29ZengMDPI AGRemote Sensing2072-42922019-04-01119102010.3390/rs11091020rs11091020Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner DataOle Martin Bollandsås0Hans Ole Ørka1Michele Dalponte2Terje Gobakken3Erik Næsset4Faculty of Environmental Science and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, NorwayFaculty of Environmental Science and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, NorwaySustainable Ecosystems and Bioresources Department, Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 San Michele all’Adige (TN), ItalyFaculty of Environmental Science and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, NorwayFaculty of Environmental Science and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, NorwayIn forest management, site index information is essential for planning silvicultural operations and forecasting forest development. Site index is most commonly expressed as the average height of the dominant trees at a certain index age, and can be determined either by photo interpretation, field measurements, or projection of age combined with height estimates from remote sensing. However, recently it has been shown that site index can be accurately predicted from bi-temporal airborne laser scanner (ALS) data. Furthermore, single-time hyperspectral data have also been shown to be correlated to site index. The aim of the current study was to compare the accuracy of modelling site index using (1) data from bi-temporal ALS; (2) single-time hyperspectral data with different types of preprocessing; and (3) combined bi-temporal ALS and single-time hyperspectral data. The period between the ALS acquisitions was 11 years. The preprocessing of the hyperspectral data included an atmospheric correction and/or a normalization of the reflectance. Furthermore, a selection of pixels was carried out based on NDVI and compared to using all pixels. The results showed that bi-temporal ALS data explained about 70% (R<sup>2</sup>) of the variation in the site index, and the RMSE values from a cross-validation were 3.0 m and 2.2 m for spruce- and pine-dominated plots, respectively. Corresponding values for the different single-time hyperspectral datasets were 54%, 3.9 m, and 2.5 m. With bi-temporal ALS data and hyperspectral data used in combination, the results indicated that the contribution from the hyperspectral data was marginal compared to just using bi-temporal ALS. We also found that models constructed with normalized hyperspectral data produced lower RMSE values compared to those constructed with atmospherically corrected data, and that a selection of pixels based on NDVI did not improve the results compared to using all pixels.https://www.mdpi.com/2072-4292/11/9/1020ALShyperspectral imagerysite indexatmospheric correctionnormalization |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Ole Martin Bollandsås Hans Ole Ørka Michele Dalponte Terje Gobakken Erik Næsset |
spellingShingle |
Ole Martin Bollandsås Hans Ole Ørka Michele Dalponte Terje Gobakken Erik Næsset Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data Remote Sensing ALS hyperspectral imagery site index atmospheric correction normalization |
author_facet |
Ole Martin Bollandsås Hans Ole Ørka Michele Dalponte Terje Gobakken Erik Næsset |
author_sort |
Ole Martin Bollandsås |
title |
Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data |
title_short |
Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data |
title_full |
Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data |
title_fullStr |
Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data |
title_full_unstemmed |
Modelling Site Index in Forest Stands Using Airborne Hyperspectral Imagery and Bi-Temporal Laser Scanner Data |
title_sort |
modelling site index in forest stands using airborne hyperspectral imagery and bi-temporal laser scanner data |
publisher |
MDPI AG |
series |
Remote Sensing |
issn |
2072-4292 |
publishDate |
2019-04-01 |
description |
In forest management, site index information is essential for planning silvicultural operations and forecasting forest development. Site index is most commonly expressed as the average height of the dominant trees at a certain index age, and can be determined either by photo interpretation, field measurements, or projection of age combined with height estimates from remote sensing. However, recently it has been shown that site index can be accurately predicted from bi-temporal airborne laser scanner (ALS) data. Furthermore, single-time hyperspectral data have also been shown to be correlated to site index. The aim of the current study was to compare the accuracy of modelling site index using (1) data from bi-temporal ALS; (2) single-time hyperspectral data with different types of preprocessing; and (3) combined bi-temporal ALS and single-time hyperspectral data. The period between the ALS acquisitions was 11 years. The preprocessing of the hyperspectral data included an atmospheric correction and/or a normalization of the reflectance. Furthermore, a selection of pixels was carried out based on NDVI and compared to using all pixels. The results showed that bi-temporal ALS data explained about 70% (R<sup>2</sup>) of the variation in the site index, and the RMSE values from a cross-validation were 3.0 m and 2.2 m for spruce- and pine-dominated plots, respectively. Corresponding values for the different single-time hyperspectral datasets were 54%, 3.9 m, and 2.5 m. With bi-temporal ALS data and hyperspectral data used in combination, the results indicated that the contribution from the hyperspectral data was marginal compared to just using bi-temporal ALS. We also found that models constructed with normalized hyperspectral data produced lower RMSE values compared to those constructed with atmospherically corrected data, and that a selection of pixels based on NDVI did not improve the results compared to using all pixels. |
topic |
ALS hyperspectral imagery site index atmospheric correction normalization |
url |
https://www.mdpi.com/2072-4292/11/9/1020 |
work_keys_str_mv |
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