Jarle Hamar Reksten

Dr. Jarle Hamar Reksten

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Research Focus & Metrics

Academic Career Length

19Years (2008-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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29 November 2018 in Archaeological Prospection
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JRJarle Hamar Reksten
Jarle Hamar Reksten
DCDave Cowley
Dave Cowley
AWAnders Ueland Waldeland
Anders Ueland Waldeland
This article presents results of a case study within a project that seeks to develop heavily automated analysis of digital topographic data to extract archaeological information and to expedite large area mapping. Drawing on developments in computer vision and machine learning, this has the potential to fundamentally recast the capacity of archaeological prospection to cover large areas and deal with mass data, breaking a dependency on human resource. Without such developments, the potential of the vast amount of archaeological information embedded in large topographic and image‐based datasets cannot be realized. The purpose of the case study reported on here is to assess existing developments in a Norwegian study against digital topographic data for the island of Arran, Scotland, examining the transferability of the approach and providing a proof of concept in a Scottish context. For Arran, three monument classes were assessed – prehistoric roundhouses, shieling huts of medieval or post‐medieval date, and small clearance cairns. These present different challenges to detection, with preliminary results ranging from a manageable mix of false positives and true identifications to the chaotic. The influence of variable morphology and the occurrence of other, largely natural, objects of confusion in the landscape is discussed, highlighting the potential improvements in automated detection routines offered by adding anthropogenic and natural false positives to additional confusion classes.

9 December 2008 in Archaeological Prospection
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JRJarle Hamar Reksten
Jarle Hamar Reksten
SLSiri Øyen Larsen
Siri Øyen Larsen
RSRune Solberg
Rune Solberg

1 January 2018 in European Journal of Remote Sensing
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Journal Article
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JRJarle Hamar Reksten
Jarle Hamar Reksten
ASArnt-Børre Salberg
Arnt-Børre Salberg
MKMartin Kermit
Martin Kermit
ØRØystein Rudjord
Øystein Rudjord
TGTerje Gobakken
Terje Gobakken
DADagrun Aarsten
Dagrun Aarsten
This article compares four new automatic methods to discriminate between spruce, pine and birch, which are the dominating tree species in Norwegian forests. Airborne laser scanning and hyperspectral data were used. The laser scanning data was used to mask pixels with low or no vegetation in the hyperspectral data. A green–blue ratio was used to remove shadow areas from tree canopies, and the normalized difference vegetation index to remove dead vegetation and non-vegetation. The best method was hyperspectral pixel classification with 160 spectral channels in the visible and near-infrared spectrum, using a deep neural network. This method achieved 87% correct classification rate. Partial least squares regression for hyperspectral pixel classification achieved 78%. Deep neural network image classification using canopy height blended with three hyperspectral channels achieved 74%. A simple pixel classification method based on two spectral indices resulted in 67% correct classification. A possible future improvement is to find a better way to combine hyperspectral data with canopy height data in a deep neural network.

4 April 2012 in Archaeological Prospection
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JRJarle Hamar Reksten
Jarle Hamar Reksten
LPLars Holger Pilø
Lars Holger Pilø

1 January 2018 in European Journal of Remote Sensing
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JRJarle Hamar Reksten
Jarle Hamar Reksten
ASArnt Salberg
Arnt Salberg
JHJörg Haarpaintner
Jörg Haarpaintner
DADagrun Aarsten
Dagrun Aarsten
TGTerje Gobakken
Terje Gobakken
ENErik Næsset
Erik Næsset
This paper proposes a new method for mapping of forest cover in Tanzania, in the form of yearly estimates of average vegetation height from time-series of Landsat and ALOS PALSAR satellite images. By using airborne laser scanning data and Landsat-8 data from 2014, a regression between average vegetation height and the specific leaf area vegetation index is established. By using all available Landsat acquisitions of the same area within 1 year, and producing a yearly estimate of vegetation height, the estimation error variance is reduced. The variance is further reduced by Kalman filtering the sequence of yearly estimates. A multi-sensor version of the method comprises application of the radar backscatter when L-band SAR data is available. To conclude, we have demonstrated that estimation of mean vegetation height is possible from dense time series of optical and SAR satellite data. Change detection was able to detect areas with total loss of biomass.

25 October 2024 in Remote Sensing
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JRJarle Hamar Reksten
Jarle Hamar Reksten
ASArnt Salberg
Arnt Salberg
The Norwegian Environment Agency is responsible for updating a map of undisturbed nature, which is performed every five years based on aerial photos. Some of the aerial photos are already up to five years old when a new version of the map of undisturbed nature is published. Thus, several new nature interventions may have been missed. To address this issue, the timeliness and mapping accuracy were improved by integrating Sentinel-2 satellite imagery for the detection of new roads across Norway. The focus on new roads was due to the fact that most new nature interventions include the construction of new roads. The proposed methodology is based on applying U-Net on all the available summer images with less than 10% cloud cover over a five-year period, with an aggregation step to summarize the predictions. The observed detection rate was 98%. Post-processing steps reduced the false positive rate to 46%. However, as the false positive rate was still substantial, the manual verification of the predicted new roads was needed. The false negative rate was low, except in areas without vegetation.