-------------------------------------------------------------------- (c) Lazaros Oreopoulos 7/99 Last modified 10/99 -------------------------------------------------------------------- The 2D cloud field for this experiment is from an Independent Approxi- mation retrieval on a 128x128 segment of a Landsat-4 scene used in Oreopoulos and Davies, J. Climate, 11, 919-932, 1998, originally provided kindly by B. Wielicki of NASA Langley. Band 4 (0.83 microns) was used. For the retrievals the ocean surface albedo was set 0.043 (i.e. to the reflectance of raw count value =15 for the 29 degree SZA at the time of the observation). Thus, an optical depth of zero was assigned to all pixels with count values less than 16. Liquid water phase was assumed throughout, and a lognormal dropsize distribution with re=10 microns and effective variance 0.15 was used to construct the look-up tables. Atmospheric effects were neglected in the retrievals. Note that some pixels (~2.5%) are saturated (raw count=255) The optical depth field consists of 128 vertically homogeneous pixels along the x- and y-directions, with a horizontal width of 30 m in both directions (it can be viewed in scene43.tau.128x128.jpg and downloaded as scene43.tau.128x128.gz ). Consider a flat cloud bottom at 0.2 km and cloud top heights determined from the geometrical thickness field given in scene43.dz.128x128.gz (it can be viewed in scene43.dz.128x128.jpg). The geometrical thickness field was derived with the aid of the brightness temperature field (scene43.band6.bt.128x128.jpg) and the optical depth field. The raw band 4 count field from which can be viewed in scene43.band4.128x128.jpg. The mean cloud optical depth (cloudy part) is 11.4 and the standard deviation is 10.6; the cloud fraction is 0.884. A sample Fortran code that reads the optical depth field follows: c----------------------------------------------------------------- parameter (nx=128, ny=128) open (11, file='scene43.tau.128x128', status='old') c Read in optical depth c c Read along the y-direction first (high to low y-coordinates) c then along the x-direction (low to high coordinates) do iy=1,ny read (11, '(128f7.2)') (tau(ix,iy), ix=1,nx) enddo close(11) c------------------------------------------------------------------ Description of experiments -------------------------- ASSUMPTIONS: 1) No atmospheric effects 2) Periodic boundary conditions (cloud field is repeated an infinite number of times along the x and y directions) 3) Henyey-Greenstein phase function (PF) with g=0.85 4) Black (zero reflectance) surface 5) Single scattering albedos w0=1 and w0=0.99 (with the same PF and extinction field). SOLAR GEOMETRY: 1) Sun at zero degrees 2) Sun at 60 degrees and 0 azimuth (Sun shining along the x axis from low x coordinates) This makes a total of 2x2=4 experiments: Exp.# 1: SZA = 0, w0 = 1 2: SZA = 60, w0 = 1 3: SZA = 0, w0 = 0.99 4: SZA = 60, w0 = 0.99 Required output --------------- 1) Mean, and higher order moments of: albedo (R) transmittance (T) absorptance (wherever applicable) (A) net horizontal flux (H) defined as 1-R-T-A nadir reflectivity (Iu) defined as pi*Nu/(F*mu0) where Nu is the upward exiting radiance at 0 degrees, mu0 is the cosine of the solar zenith angle, and F(=1) is the incident solar flux zenith transmissivity (Id) defined as pi*Nd/(F*mu0) where Nd is the downward exiting radiance at 180 degrees !!! This quantity is requested only when SZA=60!!! Higher order moments are calculated as sum_i(x_i-x_mean)^k/N, k=2,6 and N=128x128, i=1,N. The accuracy of all output means should be at least 0.001 (feel free to perform calculations of higher accuracy, and whenever possible please document your uncertainty values). All the above quantities (except A and H) are registered at cloud boundaries (highest cloud top for albedo and reflectivity and cloud base for transmittance and transmissivity). Directional tolerance (angular width of radiation "pencil") for reflectivity and transmissivity is left up to the user, but must be documented and provided when the results are submitted. Plan also for a file that will include CPU time for each experiment. In order to evaluate code performance as opposed to hardware performance we'll need to normalize with your machine's SPECfp_base95; you can look up your computer at http://www.specbench.org/osg/cpu95/results/cfp95.html, click at the HTML link for it and pull out the SPECfp_base95 number. Please submit the SPECfp_base95, and the CPU and "wall clock" (real elapsed) times for each experiment. For UNIX platforms CPU time can be obtained by using the time or timex commands; see your man pages for specific options. Formats and file name conventions can be found below. ************************** How to submit your results ************************** ------------------------Name convention------------------------ a) Fields of radiative quantities ================================= Create a separate file for each experiment and output field. Use the following name convention: I3RC_RQ_case_exp#.inst[n] where: i) "RQ" is the radiative quantity contained the file. RQ takes the following values: RQ=R (reflectance) RQ=T (transmittance) RQ=A (absorptance) RQ=H (net horizontal flux) RQ=Iu (nadir reflectivity) RQ=Id (zenith transmissivity) ii) "case" is the cloud field case For phase I the cloud field cases have been assigned the following numbers: case=1 step cloud case=2 MMCR-retrieved cloud case=3 Landsat-retrieved cloud Thus, for this field, put case=3 iii) "exp#" is the experiment number as listed above; valid numbers are 1-4 for this case iv) "inst" is the four-letter code that has been assigned to each institution participating in the experiment. The codes are listed in filename_TBD . v) "[n] is an index number following the institution whenever there are more than one participant or codes from the same institution. There is is no number for institutions with one participant and one code. We have already notified participants that have index numbers. ****Examples**** 1) The nadir reflectivity field of experiment 4, Landsat cloud case submitted by a participant affiliated with institution AESC should have the following filename: I3RC_Iu_3_4.AESC 2) The reflectance field of experiment 2, MMCR cloud case submitted by the 2nd participant of institution UMBC should be put in the following file: I3RC_R_3_2.UMBC2 b) Statistics of radiative quantities ===================================== Create a separate file for each experiment. This file will contain the statistics of all radiation quantities. Use the following convention: I3RC_fname_case_exp#.inst[n] where fname="stats" (without the quotes) and the rest is as before. c) Mean and pixel-level errors ========================================= Create a separate file for each experiment. This file will contain the mean pixel-level error and the error to the mean. Use the following convention: I3RC_fname_case_exp#.inst[n] where fname="errors" (without the quotes) and the rest is as before. d) Computing performance ======================== Create a single file for the experiment. This file will contain CPU time information for each experiment. Use the following convention: I3RC_fname_case_inst[n] where fname="CPER" (uppercase, without the quotes) and the rest is as before. ------------------------Output format------------------------- 1) For each field create a file using output format as the one produced by the following Fortran code --------------------------------------------------------------- parameter (nx=128, ny=128) real R(nx,ny) open (11, file='I3RC_R_3_1_UCOL1', status='unknown') do iy=1,ny write (11, '(128f8.4)') (R(ix,iy), ix=1,nx) enddo ----------------------------------------------------------------