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

Table of Contents

1. Contacts and Acknowledgments:

Investigator(s) Name and Title:

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

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

Vegetation Radiance

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