pixel scale validation and ground truth of satellite-based surface energy flux products myths vs...
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1/21/2016 Pixelscale Validation and Ground truth of Satellitebased Surface Energy flux products: Myths vs. Reality | Ramesh Dhungel | LinkedIn
https://www.linkedin.com/pulse/pixelscalevalidationgroundtruthsatellitebasedsurfacedhungel?trk=profpost 1/23
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Pixelscale Validation and Ground truth of Satellitebased Surface Energy flux products: Myths vs.RealityJan 21, 2016 173 views 3 Likes 0 Comments
In this era of publication, “Publish or Perish” (Prof. AnneWil Harzing), we have
to deal with the popular term “Calibration and Validation” of the model every day.
If the model had been already developed and validated, we need to compare the
results to different groundbased point scale data. In case of the satellite based
surface energy flux products, mostly the products are compared to the flux
towers, weather stations or independently setup stations. The satellite based
product helps us to gain a greater understanding of the different surface energy
fluxes in larger spatial and temporal resolution, but it has limitations.
For example, if we are calculating evapotranspiration (ET) from the satellite
based model ( 30 m scale for Landsat), the fundamental terms ( i.e. solar
radiation, precipitation, incoming and outgoing radiation, surface and air
temperature, soil moisture etc. at various heights as well as various spatial and
Ramesh DhungelWater Resources, Remote Sensing and LandSurface Modeler (LSM) (Ph.D. Civil Engineering)
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Pixelscale Validation andGround truth of SatellitebasedSurface Energy flux products:…Myths vs. RealityRamesh Dhungel
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1/21/2016 Pixelscale Validation and Ground truth of Satellitebased Surface Energy flux products: Myths vs. Reality | Ramesh Dhungel | LinkedIn
https://www.linkedin.com/pulse/pixelscalevalidationgroundtruthsatellitebasedsurfacedhungel?trk=profpost 2/23
temporal resolutions) that we are dealing are shown in the cartoon below
(Dhungel, 2014). ET is only one out of the other numerous hydrological
products. But the vital question is how many of these indirect products (in
cartoon below) can be calculated/measured accurately to get the precise final
pixelscale ET product. Now, we already have a long list of
assumptions/hypothesis/postulations which may have already been
published/cited/presented, so that we can ignore/adjust/interpret many of these
terms to accommodate final product, right? We will show the r2, R2, RMSE
etc.values to publish report/manuscript and evaluate our work.
Components of Evapotranspiration (ET) CalculationCartoon (Adopted from
Dhungel, 2014)
The major concern may be the accuracy the surface energy fluxes measured/
calculated from flux tower and weather stations which are used as a truth. Each
pixel can have a unique property and adjacent pixels can vary drastically based on
their unique physical properties (cartoon above). If we assume flux tower data are
accurate enough, can some of these data tell stories of million or even billion
pixels within the acceptable accuracy. In reality, pixelscale validation/calibration
and comparison of millions of pixels with ground based stations are always
challenging.
Now comes a human expert eye to evaluate the pixelscale product. An irrigation
engineer may know about the irrigation scheduling, but probably knows little
about regional climate (i.e. Radiation and precipitation, etc.). Similarly,
environmental scientist may know about flux towers, but probably less about
remote sensing. A soil scientist may know about the soil moisture, but probably
Dash's CommentsWade G. Morgan
1/21/2016 Pixelscale Validation and Ground truth of Satellitebased Surface Energy flux products: Myths vs. Reality | Ramesh Dhungel | LinkedIn
https://www.linkedin.com/pulse/pixelscalevalidationgroundtruthsatellitebasedsurfacedhungel?trk=profpost 3/23
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Ramesh Dhungel
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less about the turbulence process. Finally, a remote sensing scientist may know
the remote sensing process/ algorithm/ programming, but not necessarily know
all the landsurface process to calculate ET (or other processes). So,
another reality, we are judging/comparing a pixelscale fluxes by different eyes
with numerous uncertainties. We have to be very careful while evaluating the
final pixelscale product and draw a conclusion (who is evaluating irrigation
engineer/ regional climate expert/ environmental scientist/ remote sensing
expert/ soil scientist). We can be lucky enough to get a hydrologist who is an
expert in all of these terms, probably yes or no? We can answer ourselves.
References
Dhungel, R.; Allen, R. Time Integration of Evapotranspiration Using a Two
Source Surface Energy Balance Model Using NARR Reanalysis Weather and
Satellite Based METRIC Data. Ph.D. Thesis, University of Idaho, Kimberly, ID,
USA, 2014
http://www.harzing.com/pop.htm
https://www.researchgate.net/publication/277324032_Time_Integration_of_Evapotranspiration
The Crazy Story of What Really Went Wrong atTarget CanadaJan 22, 2016 129 Likes 27 Comments
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