SEBAL - Dca.ufcg.edu.br

Appendix 8Iteration Spreadsheet Used for the Atmospheric Stability CorrectionThe SEBAL process described in this manual includes a spreadsheet named“Calculations_for_05_H_Automatic_GMD_model.xls” that is used to facilitate the iterationprocess used in SEBAL for the correction of the aerodynamic resistance to heat transport(r ah ) due to buoyancy effects in the atmosphere. In SEBAL, first, initial values for the frictionvelocity (u * ) and r ah are computed assuming neutral atmospheric conditions. The sensibleheat flux (H) is computed next. Then, using the Monin-Obukhov theory, u * and r ah arecomputed again using the stability correction. The corrected r ah is then used to compute anew dT function and a new value for H. This iteration is repeated until dT and r ah at the“hot” pixel stabilize.In the SEBAL process and ERDAS Imagine Model Maker, the iterative process can bedone manually, i.e., an updated Imagine model (for example, “F13_h_1.gmd”) is operatedduring each iteration. Alternatively, the iterative process for H can be done automaticallyfor all iterations using the “F13toF24_h_automatic.gmd” model. In both cases, thespreadsheet is useful for calculating the correlation coefficients b and a of the dT functionthat is used for the calculation of H inside SEBAL.The spreadsheet calculates values for H cold , dT cold , H hot and dT hot . The correlationcoefficients b and a for the dT function are computed and a corrected value for T a and ρ arethen calculated. As the iteration continues with stability corrections, new values for dT coldand dT hot are calculated along with new coefficients, b and a.On the following page is an example of the iterative spreadsheet followed by instructionsfor the manual operation and the automatic operation of the process.80