Surface flux estimation using radiometric temperature: A dual‐temperature‐difference method to minimize measurement errors

Abstract

Abstract. Surface temperature serves as a key boundary condition that defines the partitioning of surface radiation into sensible and latent heat fluxes. Surface brightness temperature measurements from satellites offer the unique possibility of mapping surface heat fluxes at regional scales. Because uncertainties in satellite measurements of surface radiometric temperature arise from atmospheric corrections, surface emissivity, and instrument calibrations, a number of studies have found significant discrepancies between modeled and measured heat fluxes when using radiometric temperature. Recent research efforts have overcome these uncertainties and in addition have accounted for the difference between radiometric and aerodynamic temperature by considering soil and vegetative-canopy aerodynamic resistances. The major remaining obstacle to using satellite data for regional heat flux estimation is inadequate density of near-surface air temperature observations. In this paper we describe a simple, operational, double-difference approach for relating surface sensible heat flux to remote observations of surface brightness temperature, vegetative cover and type, and measurements of near-surface wind speed and air temperature from the synoptic weather network. A double difference of the time rate of change in radiometric and air temperature observations is related to heat flux. This double-difference approach reduces both the errors associated with deriving a radiometric temperature and with defining meteorological quantities at large scales. The scheme is simpler than other recent approaches because it requires minimal ground-based data and does not require modeling boundary layer development. The utility of this scheme is tested with ground-based radiometric temperature observations from several arid and subhumid climates with a wide range of vegetative cover and meteorological conditions. In a recent review on monitoring evaporation with remote sensing, Kustas and Norman [1996] conclude that obtaining reliable estimates of the heat fluxes using remotely sensed surface radiometric temperature TR(0) at a viewing angle 0 from remote brightness temperature measurements has been hampered by several factors. These include correcting the remotely sensed brightness temperatures for atmospheric and emissivity effects, calibration issues, and the nonuniqueness of the aerodynamic-radiometric temperature relationship due to 2263

Estimation of evapotranspiration of temperate grassland based on high-resolution thermal and visible range imagery from unmanned aerial systems

“…In this study, we applied the two-source energy balance (TSEB) model developed by Norman, Kustas, and Humes (1995). The basic idea of this and other two source EB models is to solve explicitly the problem of the ambiguity of the relationship between aerodynamic and radiometric temperature by separating surface temperature, radiative and turbulent fluxes, as well as resistances into a canopy and soil component (Shuttleworth and Wallace 1985; Norman, Kustas, and Humes 1995; Anderson et al 1997; Anderson et al 2007; Norman et al 2000). Due to the more detailed treatment of the radiative exchange and energy fluxes between the two components, the parameterization of these models is more complex and requires more input data.…”

Evaluating the two-source energy balance model using local thermal and surface flux observations in a strongly advective irrigated agricultural area

“…The net radiation divergence equation used in the DTD formulation in Norman et al [11] assumes an exponential decay of bulk R N through the canopy layer, which is simpler than the TSEB radiation formulations that separately consider both shortwave and longwave transfer through the canopy elements. The most recent equations for estimating the aerodynamic resistances above the canopy and above the soil surface are referenced in Norman et al [11].…”

“…Details of the derivation of the DTD model are described in Norman et al [11]. Briefly, the two-source-time-integrated equations of Anderson et al [27], currently called the Atmosphere-Land-Exchange-Inverse (ALEXI) model using the TSEB formulations of Norman et al [1], are used to form a double difference of radiometric and air temperatures so that an estimate of sensible heat flux can be obtained from measurements of surface radiometric temperature, air temperature, and wind speed, and estimates of vegetation height, fractional cover, type and approximate leaf size.…”

“…The most recent equations for estimating the aerodynamic resistances above the canopy and above the soil surface are referenced in Norman et al [11].…”

“…Another methodology uses time-differencing techniques to reduce the sensitivity to the requirement of an absolute LST-air temperature difference. A simplified form of a temperature-differencing approach, called the Dual-Temperature-Difference (DTD) scheme, was developed for routine applications using continuous ground-based or geostationary satellite observations of LST [11,12]. The land-surface scheme in the DTD is based on the Two-Source Energy Balance (TSEB) model framework of Norman et al [1], which accounts for the main physical factors causing differences between aerodynamic temperature and radiometric LST [13].…”