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
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.
|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|
Data are available as comma-delimited text files.
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.
hv66rad.txt: 4 Kb
hv71rad.txt: 4 Kb
hvthaw94.txt: 2.5 Kb
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:
Data collection points were 100 m apart and are referenced by Universal Transverse Mercator (UTM) Zone 6 locations.
The data were collected during 1994.
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.
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
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.
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.
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.
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.
|Easting UTM||Northing UTM||Thaw Depth (cm) 14-Jun-94||Thaw Depth 25-Jun-94||Thaw Depth 17-Jul-94|
Note: Missing data are indicated by the value -999.
|Easting UTM||Northing UTM||Time||NIR Reference||Red Reference||NIR Target||Red Target|
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.
NIR: Near Infrared
UTM: Universal Transverse Mercator