Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2006
Publication Date: February 15, 2007
Citation: Anderson, M.C., Kustas, W.P., Norman, J.M. 2007. Upscaling flux observations from local to continental scales using thermal remote sensing. Agronomy Journal. 99:240-254. Interpretive Summary: To quantify water and energy balance at the field, watershed, and regional scales for operational hydrologic assessments, we need to find reliable means for upscaling discrete (point or transect) measurements made at meteorological flux towers or with flux aircraft to full 2-dimensional coverage over the area of interest. Land-surface modeling based on remote sensing is the obvious means to achieve this kind of upscaling. In this paper, we overview a series of modeling experiments that have successfully bridged this gap between the measurement and application scales. The remote sensing model employed uses ground and satellite data that are commonly available, and is therefore well-suited for routine upscaling. Tower and aircraft flux data from field experiments in Oklahoma and Iowa are compared with flux maps created with the multi-scale ALEXI/DisALEXI modeling system, showing excellent agreement. The paper describes how this modeling system adds crucial spatial context to intensive field experiments, by providing maps of surface conditions at both smaller (e.g., field) and larger (e.g. state-continent) scales. We also explore how pre-campaign flux mapping can be used to optimally configure instrument deployment over the experimental area.
Technical Abstract: A number of recent intensive and extended field campaigns have been devoted to the collection of land-surface fluxes from a variety of platforms, with the purpose of inferring the long-term carbon, water, and energy budgets over large areas (watershed, continental, or global scales). One approach to flux upscaling is to use land-atmosphere-transfer-schemes (LATS) linked to remotely-sensed boundary conditions as an intermediary between the sensor footprint and regional scales. In this capacity, we examine the utility of a multi-scale LATS framework that uses thermal and visible/near infrared remote sensing imagery from multiple satellites to partition surface temperature and fluxes between the soil and canopy. Findings are summarized from upscaling exercises using tower and aircraft flux data collected at three experiment sites in Oklahoma and Iowa, each with a different configuration of instrumentation. Combined, the two flux-monitoring systems were found to be complementary: the towers provided high spatial resolution, time-continuous validation at discrete points within the modeling domain, while with the aircraft data it could be confirmed that the model was reproducing broad spatial patterns observed at specific moments in time. High-resolution flux maps created with the LATS allowed evaluation of differences in footprint associated turbulent, radiative, and conductive flux sensors, which may be contributing to energy budget closure problems observed with eddy correlation systems. The ability to map fluxes at multiple resolutions (1m to 10 km) with a common model framework is beneficial in providing spatial context to an experiment by bracketing the scale of interest. Multi-scale maps can also assist in the experimental design stage, in a priori assessments of sensor representativeness in complex landscapes.