Thaw Depth and Vegetation Radiance Measurements, Happy Valley, AK, 1994

Summary

This data set contains measurements for permafrost active layer thaw depth and vegetation reflectance (red and near-infrared bandwidths) at the Happy Valley Flux Study Site in northern Alaska during the summer of 1994. Sampling was conducted in a 1000-m square grid pattern, with sample points spaced 100 m apart. Median values for thaw depths were determined from five replicate measurements using a thaw probe. Dates of thaw depth measurements were 1994-06-14, 1994-06-25 and 1994-07-17. Vegetation radiance values are averages of five measurements collected from an area approximately 5m² at each grid point. Radiometric measurements were collected with Exotech-100BX, 4-channel radiometers fit with spectral filters corresponding to the SPOT/HRV-XS satellite bandwidths. Dates of radiance measurements were 1994-06-06 and 1994-07-01.

Data are available for ordering through NCAR

Citing These Data:

Oechel, W.C., Hope, A.S., Stow, D.A., and J.B. Fleming. 2003. Thaw depth and vegetation radiance measurements, Happy Valley, AK, 1994. Boulder, CO: National Center for Atmospheric Research.

Overview Table

Category Description
Data format Comma-delimited text files
Spatial coverage and resolution Happy Valley Flux Study Site, Happy Valley, Alaska, USA
Temporal coverage and resolution Dates of collection were between 1994-06-06 and 1994-07-17
File size 2.5 - 4 Kb
Parameter(s) Thaw depth and vegetation spectral radiance

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. References and Related Publications
4. Document Information

1. Contacts and Acknowledgments:

Investigator(s) Name and Title:

Walter C. Oechel, Ph.D.
Global Change Research Group
San Diego State University
Department of Biology
5500 Campanile Ave.
San Diego, CA USA 92182-0001
Phone: (619) 594-4818 x6613
E-mail: oechel@sunstroke.sdsu.edu

Allen S. Hope, Ph.D.
Department of Geography
San Diego State University
5500 Campanile Drive
San Diego, CA USA 92182-4493
Phone: (619) 594-2777
Email: hope1@mail.sdsu.edu

Douglas A. Stow, Ph.D.
Department of Geography
San Diego State University
5500 Campanile Drive
San Diego, CA USA 92182-4493
Phone: (619) 594-5498
FAX: (619) 594-4938
Email: stow@mail.sdsu.edu

J.B. Fleming

Technical Contact:

2. Detailed Data Description:

Format:

Data are available as comma-delimited text files.

File Naming Convention:

hv66rad.txt: This file contains red and NIR bandwidth radiance values (Watts per square meter) of vegetation, measured at points on a grid referenced by UTM coordinates at Happy Valley, AK, on 1994-06-06.

hv71rad.txt: This file contains red and NIR bandwidth radiance values (Watts per square meter) of vegetation, measured at points on a grid referenced by UTM coordinates at Happy Valley, AK, on 1994-07-01.

hvthaw94.txt: This file contains median thaw depth values (centimeters) measured at points on a grid referenced by UTM coordinates at Happy Valley, AK, on 1994-06-14, 1994-06-25 and 1994-07-17.

File Size:

hv66rad.txt: 4 Kb

hv71rad.txt: 4 Kb

hvthaw94.txt: 2.5 Kb

Spatial Coverage:

Data were collected at the Happy Valley Flux study Site, Happy Valley, Alaska, United States of America.

Sampling was conducted in a square grid pattern defined in Eastings and Northings:

NW: 426,400 m 7,671,700 m

SW: 426,400 m 7,671,600 m

NE: 426,500 m 7,671,700 m

SE: 426,500 m 7,671,600 m

An eddy correlation tower is located approximately at the center of the grid at the following coordinates:

69º08.54' N

148º50.47' W

Spatial Resolution:

Data collection points were 100 m apart and are referenced by Universal Transverse Mercator (UTM) Zone 6 locations.

Temporal Coverage:

The data were collected during 1994.

Temporal Resolution:

Thaw depths were measured on 1994-06-14, 1994-06-25, and 1994-07-17.

Radiometric measurements were collected on 1994-06-06 and 1994-07-01.

Parameter or Variable:

Parameter Description:

Thaw depth: During each sampling date, five measurements per grid point were collected and the median value was reported. Measurements were read from the top of the moss layer within inter-tussocks from an area approximately 5m².

Vegetation spectral radiance values: Radiances were derived from measured analog voltages and calibration coefficients provided by Exotech, Inc. The target (vegetation) radiances are averages of five measurements collected from an area approximately 5m² at each grid point. The radiometer was held approximately 1.2 meters above the ground in a nadir direction using 15º field-of-view objectives.

Reference radiance values: Reference radiances were collected from a BaSO4 reflectance panel. The radiometer was held in a nadir direction approximately 0.7 meters above the panel. The following third order polynomial describes the relationship between the bidirectional reflectance factor of the panel to solar zenith angle:

r = (a0) + (a1)T + (a2)T² + (a3)T³
where,
r = bidirectional reflectance and T = solar zenith angle

For the red channel:
a0 = 1.017597; a1 = -4.077271x10-3; a2 = 7.370045x10-5 ; a3 = -6.514387x10-7,

For the NIR channel:
a0 = 0.9980405; a1 = -3.758709x10-3; a2 = 6.606596x10-5; a3 = -5.880711x10-7

Weather conditions during radiometry were sunny and warm for both dates.

Unit of Measurement:

Radiance values for red and NIR bandwidths were measured in watts/m2.

Thaw depth was measured in centimeters.

Time (local) was recorded in hours, for example, 9.6358 = 9:38 a.m. Local solar noon is approximately 14.0000 hours.

Parameter Source:

Thaw depth measurements were taken with a 1-m thaw probe.

Radiometric measurements were collected with Exotech-100BX, 4-channel radiometers fit with spectral filters corresponding to the SPOT/HRV-XS satellite bandwidths (green, red, and NIR). The fourth channel was fit with the spectral bandwidth corresponding to Landsat-TM blue. Only red and NIR measurements are reported here.

Parameter Range:

Thaw depth ranged from 4 to 64 cm.

Spectral radiance of vegetation in the NIR bandwidth ranged from 11.02 to 22.86 W/m2.

Spectral radiance of vegetation in the red bandwidth ranged from 2.35 to 6.03 W/m2.

Sample Data Record:

Thaw Depth

Easting UTM Northing UTM Thaw Depth (cm) 14-Jun-94 Thaw Depth 25-Jun-94 Thaw Depth 17-Jul-94
426000 7671700 7 12 23
426000 7671800 6 11 23
426000 7671900 6 10 24
426100 7672100 -999 -999 -999

Note: Missing data are indicated by the value -999.

Vegetation Radiance

Easting UTM Northing UTM Time NIR Reference Red Reference NIR Target Red Target
426000 7671400 12.1356 53.16 63.65 18.99 4.78
426000 7671500 12.0944 52.99 63.38 19.49 5.23
426000 7671600 11.4519 49.99 59.65 20.67 5.49

3. References and Related Publications:

Hope A.S., Fleming J.B., Vourlitis G.L., Stow D.A., Oechel W.C., and T. Hack. 1995. Relating CO2 fluxes to spectral vegetation indices in tundra landscapes: Importance of footprint definition. Polar Record 31: 245-250.

Hope A.S., McMichael C.E., Stow D.A., Fleming J.B., Vourlitis G., Oechel W.C., and S. Hastings. 1995. Direct estimates of CO2 flux in arctic environments using a spectral vegetation index. Proceedings IGARSS'97 Conference, Florence Italy.

McMichael C.E., Hope A.S., Stow D.A., and J.B. Fleming. 1997. The relationship between active layer depth and a spectral vegetation index in arctic tundra landscapes of the North Slope of Alaska. International Journal of Remote Sensing 18(11): 2371-2382.

McMichael C.E., Hope A.S., Stow D.A., Fleming J.B., Vourlitis G.L., and W.C. Oechel. 1999. Estimating CO2 exchange at two sites in Arctic tundra ecosystems during the growing season using a spectral vegetation index. International Journal of Remote Sensing 20(4): 683-698.

4. Document Information:

Glossary and Acronyms:

Acronyms:

NIR: Near Infrared

UTM: Universal Transverse Mercator

Document Creation Date:

2003-02-04