SEBAL - Dca.ufcg.edu.br

More documents

Recommendations

Info

Tendency of vertical movement of air at near land surface,assuming 6.5 o C/km air lapse rate19.35 o C19.7 o C19.35 o C19.35 o C19.35 o C19.1 o C100m20 o C 20 o C20 o C 20 o C 20 o C 20 o CUnstableN eutralStable: Direction of Force: Direction of Sensible Heat FluxRelative shapes of eddy at near land surfaceUnstableN eutralStableFigure 11.1. Three Conditions of Atmospheric Stability92
Appendix 12The SEBAL Mountain ModelSEBAL provides accurate estimations of ET for relatively flat agricultural areas. For use inmountainous areas where there is significant relief and a wide range of slopes and aspects,the SEBAL Mountain Model was developed. The SEBAL Mountain Model containsmodifications that correct for slope, aspect, and elevation in the computations. The 24-hoursolar radiation is typically much higher on a south slope than on a north slope in theNorthern Hemisphere. The result of not making the corrections for slope, aspect, andelevation is that a higher than actual ET will be computed for north slopes and highelevations because SEBAL incorrectly interprets the cooler surface temperatures asindicating “wet” (therefore cool) areas. The cooler surface temperatures on north facingslopes and high elevations is not due to “wetness” however, but is from the temperaturelapse caused by higher elevation and from less incident solar radiation caused by theaspect.Predictions of air flow and wind speed over mountainous areas are much more difficult. Theeffects from the orthographic drainage of air caused by cooling, the acceleration of airstreams passing over mountains due to the venturi effect, and the impacts of drag due toundulating topography all combine to make wind speed prediction difficult and complicated.The following describes the modifications that are made to the SEBAL Flat Model in orderfor it to be used in mountainous areas (SEBAL Mountain Model):A. Data RequirementsA Digital Elevation Model (DEM) is required to provide elevation data. The units of the DEMshould be in meters with a pixel size the same as that of the satellite data (30m × 30m). Asin the flat model, a layered image must first be created followed by a smaller subset imageif desired (Appendix 4). A DEM subset image must then be created which is the same sizeas the subset image. To do this, one must go to the ERDAS Data Prep-subset image tooland input the DEM from a disk and enter the coordinates of the subset image. The outputwill be the DEM subset image.B. Slope and Aspect ImagesThe Mountain Model requires slope and aspect information for its computations. The slopeand aspect for each pixel are derived using the DEM subset image and the ERDASInterpreter–topographic analysis–slope/aspect tool. The slope and aspect images are thensaved as the output.C. Calculation of the Cosine of the Solar Incidence Angle (cos θ)The solar incidence angle is the angle between the solar beam and a vertical lineperpendicular to the land surface. In the flat model, we assume that the land surface ishorizontal and the calculation of cos θ is very simple and is a constant over the area ofinterest. In the Mountain Model, cos θ is different for each pixel depending on the slope and93
Page 1 and 2:
SEBALSurface Energy Balance Algorit
Page 3 and 4:
6. Tables for surface albedo comput
Page 5 and 6:
δ declination of the earth radians
Page 7 and 8:
INTRODUCTION1. BACKGROUNDLand manag
Page 9 and 10:
THE THEORETICAL BASIS OF SEBAL1. OV
Page 11 and 12:
The surface emissivity is the ratio
Page 13 and 14:
• Reference evapotranspiration, E
Page 15 and 16:
Figure 3. Flow Chart of the Net Sur
Page 17 and 18:
2. The reflectivity for each band (
Page 19 and 20:
and ET are specified for the two ex
Page 21 and 22:
To complete step 2, model F06_surfa
Page 23 and 24:
D. Choosing the “Hot” and “Co
Page 25 and 26:
irrigated crops near Kimberly, Idah
Page 27 and 28:
where; u * is the friction velocity
Page 29 and 30:
Weather stationu, z x, z om, u *H f
Page 31 and 32:
Note: An alternative method used by
Page 33 and 34:
where;⎛ 2 ⎞⎜1+ x(0.1m)Ψ = 2
Page 35 and 36:
where; ET inst is the instantaneous
Page 37 and 38:
Figure 6 shows an example of a dail
Page 39 and 40:
1. If there is some cloud cover in
Page 41 and 42: • For all other formats (includin
Page 43 and 44: On the main page, select Type in Pa
Page 45 and 46: These values for z om can vary by r
Page 47 and 48: Appendix 3Reference Evapotranspirat
Page 49 and 50: and click on “Open”3. Provide t
Page 51 and 52: 5. Describe weather station and wea
Page 53 and 54: 8. Save the output file using a nam
Page 55 and 56: 4. Go to the Viewer tool and view t
Page 57 and 58: Appendix 5Time Issues Around Weathe
Page 59 and 60: 2. What time interval does the data
Page 61 and 62: The wind speed is 3.4 m/s for the 1
Page 63 and 64: Table 6.3. ESUN λ for Landsat 5 TM
Page 65 and 66: Table 6.6. Typical albedo values.Fr
Page 67 and 68: 4. Make a first guess for T cold by
Page 69 and 70: Fig.3. P40/R30, Landsat 7 ETM+ 4/8/
Page 71 and 72: Fig.5. P40/R30, Landsat 7 ETM+ 4/8/
Page 73 and 74: We open the image or subset image a
Page 75 and 76: Now, we look at the northwest area
Page 77 and 78: (2) The regional weather or soil co
Page 79 and 80: We conclude that this “heat islan
Page 81 and 82: Part 1: using the manual iteration
Page 83 and 84: Part 2: Using the automatic iterati
Page 85 and 86: Appendix 9SAVI and LAI for Southern
Page 87 and 88: equation for G. The following are e
Page 89 and 90: and for 24-hours:Gwater = 0.9 Rn -
Page 91: The Stability of the AtmosphereAppe
Page 95 and 96: where; t is the standard clock time
Page 97: N. Momentum Roughness LengthThe mom
show all

SEBAL - Dca.ufcg.edu.br

Create successful ePaper yourself

Delete template?

Save as template?