VLIDORT User's Guide

to both VLIDORT and the given VSLEAVE computational subroutine. This surface-leaving testsimulates the effect of fluorescence in the spectral band 640-820nm.Section 6.2 has additional notes on the scalar and vector test cases in this installation. Appendices6.3 and 6.4 have descriptions of the VBRDF and VSLEAVE supplements.4.3.5. Helpful Tips for input settingsIn this section, we compile some useful tips for setting the inputs:1. All angles are given in degrees. Solar angles must lie in the range [0°,90°); this version ofVLIDORT is not a twilight code. Viewing zenith angles are by convention positive in therange [0°,90°], and relative azimuth angles are in the range [0°,360°]. These inputs arechecked; invalid values will cause the model to abort and generate error messages.2. Output at various vertical levels is essentially specified according to geometrical height (notoptical depth as in DISORT and earlier versions of VLIDORT). The reason for this is that theheight specification is independent of wavelength. We illustrate the convention for verticaloutput with some examples. USER_LEVELS(1) = 2.0 means that the first level for outputwill be at the bottom of the second layer in the atmosphere. USER_LEVELS(2) = 2.5 meansthat the second level of output will be halfway down the third layer. Thus if you want TOAoutput only, then you need to set USER_LEVELS(1) = 0.0. If there are 24 layers in youratmosphere and you want BOA output only, then you set USER_LEVELS(1) = 24.0. Theordering is not important; VLIDORT will make an internal "sort" of the output levels intoascending order, and the final intensities and Jacobians will be generated in the sorted order.Out-of-range levels are rejected (this is a fatal input check error).3. The number of scattering matrix expansion coefficients (NGREEK_MOMENTS_INPUT)should be at least 2N−1, where N is the number of discrete ordinates (the variableNSTREAMS). If you are using the delta-M scaling, then NGREEK_MOMENTS_INPUTshould be at least 2N (otherwise the scaling will not work). By definition, the multiplescattering fields are calculated using at most 2N−1 (possibly scaled) expansion coefficients,whereas the exact single scatter calculations will use all coefficients from 0 toNGREEK_MOMENTS_INPUT.4.4. Exception handling and utilities4.4.1. Exception handlingTable 4.6. Exception handling for the VLIDORT 2.6 code(; 0=VLIDORT_SUCCESS, 3=VLIDORT_WARNING, 4=VLIDORT_SERIOUS)Name Type Values PurposeSTATUS_INPUTCHECK INTEGER 0, 3 or 4 Overall Status of Input-checkNCHECKMESSAGES INTEGER 0 to 25 Number of Input-check Error MessagesCHECKMESSAGES CHARACTER ASCII String Array of Input-check Error MessagesACTIONS CHARACTER ASCII String Array of Input-check Actions to takeSTATUS_CALCULATION INTEGER 0 or 4 Overall Status of CalculationMESSAGE CHARACTER ASCII String Calculation Failure, MessageTRACE_1 CHARACTER ASCII String First Subroutine Trace for Place of FailureTRACE_2 CHARACTER ASCII String Second Subroutine Trace for Place of FailureTRACE_3 CHARACTER ASCII String Third Subroutine Trace for Place of Failure73