Estimation of surface heat and moisture fluxes over a prairie grassland: 4. Impact of satellite remote sensing of slow canopy variables on performance of a hybrid biosphere model

Crosson, William L.; Smith, Eric A.; Cooper, Harry J.

doi:10.1029/92jd01917

Cited by 15 publications

(8 citation statements)

References 33 publications

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“…Modifications to the original model include a redesign of the radiation scheme, a more explicit treatment of the soil thermal properties, and a more flexible treatment of the various canopy variables. The original description of Ex-BATS can be found in the work of Smith et al [1993] and Crosson et al [1993]. The canopy albedo algorithm of Sellers [1985] has been since incorporated into the model.…”

Section: Description Of Biosphere-atmosphere Exchange Modelmentioning

confidence: 99%

Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Cooper¹,

Smith²,

Gu³

et al. 1997

J. Geophys. Res.

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variability and intensity of surface and subsurface fluxes of heat and moisture and showed that they exerted a significant influence on mesoscale dynamics over the relatively small (15 x 15 km) FIFE study area.The problem of properly assimilating small-scale fluxes into large-scale models has also received considerable attention. In regional models, a single horizontal grid element can cover between 103 and 10 4 km 2, while in global climate models (GCMs), the grid size can be l0 s km 2, or larger. At these scales the spatial variation in land surface properties can be considerable. Since the physical properties of the land surface and soils exert a significant control over the spatial variability of surface fluxes and since the interaction between the land surface and the fluxes is nonlinear, linking the sub-grid-scale fluxes to larger scales is a difficult problem. Li and Avissat [1994] examined the nonlinear relationship between the spatial variability of land surface characteristics, vegetation physiology, and the resulting area-averaged heat fluxes and showed that considerable errors arise in trying to estimate grid fluxes using plant and surface properties averaged from detailed subgrid-scale inputs. 29,235

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Section: Description Of Biosphere-atmosphere Exchange Modelmentioning

confidence: 99%

Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Cooper¹,

Smith²,

Gu³

et al. 1997

J. Geophys. Res.

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“…Resolution at satellite subpoint is about 1.1 km so that the area around each station covered by the spatial averaging process is approximately 11 km 2. Cloud subgrids were eliminated using a screening process [see Crosson et al, 1993]. After the screening procedure was applied, 30 daily overpasses form 1987 and 4 days from 1989 were obtained for the analysis.…”

Section: Surface and Satellite Datamentioning

confidence: 99%

“…budget, and to heat and moisture exchanges between the land surface and the atmosphere [e.g., Wetzel et al, 1984;Wetzel and Woodward, 1987]. Recently, a four-part paper by Smith et al [1992a], Crosson and Smith [1992], Smith et al [1993], and Crosson et al [1993] reported the development of a hybrid modeling approach in which satellite-derived estimates of various surface variables are used as boundary condition inputs within a detailed biosphere-atmosphere exchange model to diagnose surface heat and moisture fluxes. This study is a follow-up to the aforementioned study in which we use the same experimental version of the biosphere-atmosphere transfer scheme (Ex-BATS) [see Smith et al, 1993] to provide estimates of sensible heat fluxes during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) in 1987 and 1989.…”

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confidence: 99%

Limitations in estimating surface sensible heat fluxes from surface and satellite radiometric skin temperatures

Cooper¹,

Smith²,

Crosson³

1995

J. Geophys. Res.

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The objective of this study is to demonstrate that by use of simple physical techniques it is possible to obtain useful skill in retrieving sensible heat fluxes by the radiometric method but only on a site‐specific basis. Sensible heat fluxes measured by Bowen ratio systems at two sites during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) 1987 and FIFE 1989 are compared to sensible heat fluxes estimated from radiometric measurements of skin temperature taken by pyrgeometers mounted 1.75 m above the surface. An experimental version of the biosphere‐atmosphere transfer scheme (Ex‐BATS), capable of reproducing statistically reliable estimates of the measured heat fluxes, is used to show that good agreement can be obtained between the model‐diagnosed surface temperatures and the skin temperatures obtained from the pyrgeometers. However, because of biases in the radiometer values which are small in an absolute sense but large in terms of the differential temperatures between surface and atmosphere, use of such temperatures in modified bulk formula expressions gives rise to significant biases in the sensible heat fluxes. By reconciling radiometric estimates of the sensible heat fluxes and the fluxes measured by the Bowen ratio systems, a mean effective emissivity considered in the form of a site‐specific calibration constant can be calculated for each of the two sites. Using the new emissivities, corrected radiometric surface temperatures are obtained that remove the biases at each site, demonstrating that the radiometric method is feasible but only on a site‐specific basis. The corrected skin temperatures are then compared to the advanced very high resolution radiometer (AVHRR)‐derived split window estimates of skin temperature obtained on 30 clear‐sky days during the 1987 experimental period. The two data sets are found to be well‐correlated but also with an underlying bias. Differences between the satellite estimated temperatures and the corrected skin temperatures are attributed to imperfections in the coefficients used in the split window equation and residual cloud contamination, as well as considerable differences in the scenes viewed by the pyrgeometers and satellite. These differences lead to significant errors in retrieving heat fluxes from the raw satellite skin temperature estimates. The estimates can be improved after applying a regression between the corrected radiometric skin temperatures obtained for the radiometers and the satellite‐derived temperatures, although because of the residual cloud effects and scene mismatch, the final RMS error is of the order of 65 W m−2. An independent application of the regression fit between the radiometer temperatures and the AVHRR‐derived temperatures derived from the 1987 data to sensible heat flux calculations for four clear‐sky days in 1989 indicates poor skill, reinforcing the notion that for satellite applications the radiometric approach is also only feasible on a site‐specific basis.

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“…In practice, few of these models can be used at regional scales with remote sensing data because of the amount of vegetation and soils information required to evaluate the necessary parameters. Attempts at bridging this gap between having a physically-based robust model simulating the energy fluxes and remote sensing providing necessary information for determining key surface parameters in an operational mode have been successful to some degree Crosson et al, 1993). Two such approaches which appear to have great potential for estimating ET operationally are discussed below in some detail.…”

Section: Numerical Modelsmentioning

confidence: 99%

“…None of the models explicitly address the issue of subpixel averaging (7). Preliminary studies (Crosson et al, 1993;Sellers et al, 1992) and some in progress using FIFE data suggest that issue 7 may be a significant problem at the 1 km scale but may average out at the 10 km scale (Norman & Divakarla, 1995). None of the current models addresses the issue of continuous surface fluxes even with clouds, but studies are in progress to combine the thermal IR remote sensing approaches discussed in this paper with mesoscale models, synoptic surface observations and microwave observations.…”

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confidence: 99%

Use of remote sensing for evapotranspiration monitoring over land surfaces

Kustas

Norman

1996

Hydrological Sciences Journal

516

258

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Monitoring évapotranspiration (ET) at large scales is important for assessing climate and anthropogenic effects on natural and agricultural ecosystems. This paper describes techniques used in evaluating ET with remote sensing, which is the only technology that can efficiently and economically provide regional and global coverage. Some of the empirical/statistical techniques have been used operationally with satellite data for computing daily ET at regional scales. The more complex numerical simulation models require detailed input parameters that may limit their application to regions containing a large database of soils and vegetation properties. Current efforts are being directed towards simplifying the parameter requirements of these models. Essentially all energy balance models rely on an estimate of the available energy (net radiation less soil heat flux). Net radiation is not easily determined from space, although progress is being made. Simplified approaches for estimating soil heat flux appear promising for operational applications. In addition, most ET models utilize remote sensing data in the shortwave and thermal wavelengths to measure key boundary conditions. Differences between the radiometric surface temperature and aerodynamic temperature can be significant and progress in incorporating this effect is evident. Atmospheric effects on optical data are significant, and optical sensors cannot see through clouds. This has led some to use microwave observations as a surrogate for optical data to provide estimates of surface moisture and surface temperature; preliminary results are encouraging. The approaches that appear most promising use surface temperature and vegetation indices or a time rate of change in surface temperature coupled to an atmospheric boundary layer model. For many of these models, differences with ET observations can be as low as 20% from hourly to daily time scales, approaching the level of uncertainty in the measurement of ET and contradicting some recent pessimistic conclusions concerning the utility of remotely sensed radiometric surface temperature for determining the surface energy balance.

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Estimation of surface heat and moisture fluxes over a prairie grassland: 4. Impact of satellite remote sensing of slow canopy variables on performance of a hybrid biosphere model

Cited by 15 publications

References 33 publications

Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Limitations in estimating surface sensible heat fluxes from surface and satellite radiometric skin temperatures

Use of remote sensing for evapotranspiration monitoring over land surfaces

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