TY - JOUR
T1 - Comparing land surface phenology derived from satellite and GPS network microwave remote sensing
AU - Jones, Matthew O.
AU - Kimball, John S.
AU - Small, Eric E.
AU - Larson, Kristine M.
N1 - Funding Information:
Acknowledgments This study was carried out with funding from the NASATerrestrial Ecology program. The AMSR-E global VOD database and associated biophysical retrievals from this study are available through the NASA NSIDC DAAC (http://nsidc.org/data/nsidc-0451.html). This work was performed at the University of Montana under contract to the National Aeronautics and Space Administration. PBO-H2O is supported by NSF EAR-1144221. NMRI data may be downloaded from http://xenon.colorado.edu/portal.
PY - 2014/7
Y1 - 2014/7
N2 - The land surface phenology (LSP) start of season (SOS) metric signals the seasonal onset of vegetation activity, including canopy growth and associated increases in land-atmosphere water, energy and carbon (CO2) exchanges influencing weather and climate variability. The vegetation optical depth (VOD) parameter determined from satellite passive microwave remote sensing provides for global LSP monitoring that is sensitive to changes in vegetation canopy water content and biomass, and insensitive to atmosphere and solar illumination constraints. Direct field measures of canopy water content and biomass changes desired for LSP validation are generally lacking due to the prohibitive costs of maintaining regional monitoring networks. Alternatively, a normalized microwave reflectance index (NMRI) derived from GPS base station measurements is sensitive to daily vegetation water content changes and may provide for effective microwave LSP validation. We compared multiyear (2007-2011) NMRI and satellite VOD records at over 300 GPS sites in North America, and their derived SOS metrics for a subset of 24 homogenous land cover sites to investigate VOD and NMRI correspondence, and potential NMRI utility for LSP validation. Significant correlations (P < 0.05) were found at 276 of 305 sites (90.5 %), with generally favorable correspondence in the resulting SOS metrics (r 2 = 0.73, P < 0.001, RMSE = 36.8 days). This study is the first attempt to compare satellite microwave LSP metrics to a GPS network derived reflectance index and highlights both the utility and limitations of the NMRI data for LSP validation, including spatial scale discrepancies between local NMRI measurements and relatively coarse satellite VOD retrievals.
AB - The land surface phenology (LSP) start of season (SOS) metric signals the seasonal onset of vegetation activity, including canopy growth and associated increases in land-atmosphere water, energy and carbon (CO2) exchanges influencing weather and climate variability. The vegetation optical depth (VOD) parameter determined from satellite passive microwave remote sensing provides for global LSP monitoring that is sensitive to changes in vegetation canopy water content and biomass, and insensitive to atmosphere and solar illumination constraints. Direct field measures of canopy water content and biomass changes desired for LSP validation are generally lacking due to the prohibitive costs of maintaining regional monitoring networks. Alternatively, a normalized microwave reflectance index (NMRI) derived from GPS base station measurements is sensitive to daily vegetation water content changes and may provide for effective microwave LSP validation. We compared multiyear (2007-2011) NMRI and satellite VOD records at over 300 GPS sites in North America, and their derived SOS metrics for a subset of 24 homogenous land cover sites to investigate VOD and NMRI correspondence, and potential NMRI utility for LSP validation. Significant correlations (P < 0.05) were found at 276 of 305 sites (90.5 %), with generally favorable correspondence in the resulting SOS metrics (r 2 = 0.73, P < 0.001, RMSE = 36.8 days). This study is the first attempt to compare satellite microwave LSP metrics to a GPS network derived reflectance index and highlights both the utility and limitations of the NMRI data for LSP validation, including spatial scale discrepancies between local NMRI measurements and relatively coarse satellite VOD retrievals.
KW - GPS
KW - Land surface phenology
KW - Microwave vegetation optical depth
KW - Normalized microwave reflectance index
KW - Remote sensing
UR - http://www.scopus.com/inward/record.url?scp=84904176748&partnerID=8YFLogxK
U2 - 10.1007/s00484-013-0726-z
DO - 10.1007/s00484-013-0726-z
M3 - Article
C2 - 24005849
AN - SCOPUS:84904176748
SN - 0020-7128
VL - 58
SP - 1305
EP - 1315
JO - International Journal of Biometeorology
JF - International Journal of Biometeorology
IS - 6
ER -