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Appendix 4Preparing the Original Satellite Image for Use in SEBALThe original Landsat image needs to be geo-rectified for use in SEBAL. This can be donelocally or by sending it to a commercial entity such as the Earth Satellite Corporation. It isrecommended that the rectified image by saved in the GeoTIF format and that nearestneighbor resampling be used during rectification to preserve spectral information.SEBAL uses the following seven bands of the spectrum:Band 1Band 2Band 3Band 4Band 5Band 6Band 7visible (blue)visible (green)visible (red)near infrarednear infraredthermalnear infraredThese bands must be layered inside ERDAS Imagine, in order, from 1 to 7 to create animage file for use in the SEBAL process. After that, a smaller subset image can be createdfor the area of interest. The steps for the layering a Landsat 7ETM+ image are as follows(Figure 4.1):1. Insert the geo-rectified disk (GeoTIF format)2. View the details• The six large files with a “t” in the name are the bands 1 - 5 and 7, in order.• The two large files with a “k” in the name are for band 6, low gain and high gainin that order (the low gain is recommended).• The large file with a “p” in the name is for band 8 (PanChromatic) and is not usedin SEBAL.3. In ERDAS, go to the Interpreter tool – Utilities - Layer stack and follow these steps:a. The input file will come from the geo-rectified CD in a geo-TIFF format.b. Create an output file having a unique name. It is recommended that the nameinclude the date, path, and row of the image.c. Add the seven layers in order beginning with band 1 (the first large “t” file). Afteradding band 5, add band 6 (the first large “k” file for low gain). Then add band 7(the last large “t” file).3. A layered image is now created.For Landsat 5TM images, layering is similar to above except that spectral bands 1 – 7 arelisted in order in the header file (Figure 4.2).To create a smaller subset image follow these steps:1. In ERDAS, go to the Data Prep tool - subset image.2. Input the image file created above.3. Create an output file name.54
4. Go to the Viewer tool and view the layered image. Go to Utility - Inquire Box and fitthe box to the desired area. Click on ‘Apply’.5. Return to Data Prep and click on ‘From Inquire Box’.6. The subset image file is now created.The area of interest can now be viewed with the ERDAS Viewer tool. The image is shownin false color. ERDAS has many tools for working with the image which the user must befamiliar with. Explaining all of these tools is outside the scope of this manual.Figure 4.1 Layering the image for Landsat 7ETM+Band 6 (low & high)Bands 1-5,755
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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: 8. Save the output file using a nam
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 and 92: The Stability of the AtmosphereAppe
Page 93 and 94: Appendix 12The SEBAL Mountain Model
Page 95 and 96: where; t is the standard clock time
Page 97: N. Momentum Roughness LengthThe mom
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