Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

Bibliographic data

Multivolume work

Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [FA-3 FOREST DAMAGE]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Spectral response from thinning cuttings measured by multitemporal satellitedata. Hâkan Olsson

Document type:: Multivolume work

Structure type:: Chapter

2. MATERIALS AND METHODS 2.1 Ground data collection The studied area is 40 km by 30 km. It is situated close to Umea in northern Sweden, with the center at 64°05' N and 20°30'E. Representatives for all owners of forest land in the area were contacted and asked for thinned forest stands and the dates for thinning. All known stands that were thinned once between august 1984 and july 1989 and were larger than 2.5 ha and more than 100 m wide were selected. After excluding 2 extremely heterogeneous stands did 44 thinnings remain. The field survey of the stands were carried out in October 1989. The tree species were Scots Pine (Pinus Silvestris), Norway Spruce (Picea Abies) and Birch (Betula spp.). Only 1 % of the stems were other deciduous species than Birch. In each stand nominally 10 sample plots were placed in a regular grid. The distance between the field plots were 40-80 m depending on stand size. A 50 m grid was chosen in the majority of the stands. No plot was placed less than 25 m from the stand border. Stem and stump diameters were measured in circular sample plots of 154 m 2 . About 20 more variables were also recorded. In 20 % of the stands, surveyed in the beginning of the study, the stump diameters were measured for 128 m 2 plots. The basal area in these stands were measured by relascope and a smaller number of field variables were recorded. The stump diameters were transformed to diameter at breast height by regression functions from the NFI. The basal area is defined as total stem cross-section area at breast hight in m 2 per hectare (ha). The basal area for the remaining trees at the year of thinning were calculated from the measured basal area 1989, using functions from the NFI. Thus, all basal areas refer to the year when the individual stand were thinned. The thinning grade is then defined as basal area cut divided with total basal area before thinning. To illustrate the spectral changes for stronger cuttings, five seed tree stands were also included in the analysis. These stands were subjectively chosen and field surveyed with the same methods as the thinnings. 2.2 Satellite data used The Swedish Space Corporation (SSC) provided the project with digital Landsat TM data from the summers 1984 - 1989, (table 1). SSC-Satellitbild did also make the geometrical precision correction to the Swedish national grid, with 20 m pixel size. Table 1. Satellite acquisitions used. Satellite Sensor Reg. date Scene Landsat 5 TM 1 aug. 1984 194/15 Landsat 5 TM 26 june 1985 193/15 Landsat 5 TM 6 june 1986 192/15 Landsat 5 TM 12 aug. 1987 192/15 Landsat 5 TM 27 june 1988 192/15 Landsat 5 TM 21 june 1989 193/15 The satellite scenes were radiometrically calibrated, using the calibration lamp onboard the satellite. The digital numbers (DN) measured in the satellite scene might be converted to physical units for spectral radiance using the following formula: Lmax - Lmin Spectral radiance = Lmin + DN * 255 The values of Lmin and Lmax used in the pre processing of this data set are found in table 2. Table 2. Calibration values for converting DN values to physical units for spectral radiance, expressed in W/ (n? *sr*pm) . channel colour spectral range(um) Lmin Lmax TM 1 blue 0.45 - 0.52 -1.50 152.10 TM 2 green 0.52 - 0.60 -2.80 296.80 TM 3 red 0.63 - 0.69 -1.20 204.30 TM 4 near-IR 0.76 - 0.90 -1.50 206.20 TM 5 middle-IR 1.55 - 1.75 -0.37 27.19 TM 7 middle-IR 2.08 - 2.35 -0.15 14.38 Thus, a data set of 36 channels were available. In the analysis phase, the TM data were handled as 12 blocks of 500 by 500 pixels, corresponding to 10 km by 10 km. For each block the data from one year was adjusted to 1:10 000 maps. The remaining scenes were manually adjusted to the reference scene with best integer pixel precision. For best fit compared to 1:10 000 maps, the data on an average had to be moved 22 m pooled distance, with a standard deviation of 22 m. One of the reasons for the remaining geometrical errors is obviously height parallaxes due to scenes from different paths, but also the 16 lines sensor swaths were sometimes displaced. 2.3 Extraction of standwise DN mean values Map coordinates were assigned to each field surveyed plot. For each plot the DN values for the pixel containing plot center, and the eight neighbour pixels, were extracted in all the 36 TM channels. Pixels already assigned to a plot were not used again. The location of the plots were now for the first time checked together with the satellite images. If a stand for a given acquisition was covered by clouds, cloud shadows or technical errors, no data were extracted for that year. To reduce the problem with mixel values at stand borders, all boarder pixels that in any channel were above the 99.9 % level in a t-test were excluded for all years and channels. This procedure eliminated 5.6 % of the stand pixels. On an average 60 pixels per stand remained, which corresponds to 2.4 ha. 2.4 Satellite data calibration functions For the between-scene calibration functions, an independent set of pixel values was systematically sampled from the studied area. The values were sampled under a forest mask obtained from thresholding in TM 5, 1989. The mask covered

Access restriction

Copyright

fullscreen: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

Multivolume work

Volume

Chapter

Chapter

Table of contents

Cite and reuse

Volume

Chapter

Image

Image fragment

Citation links

Citation recommendation