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--- intercomparisons:c2_cubiccloud [2016/11/15 16:22]
127.0.0.1 external edit
+++ intercomparisons:c2_cubiccloud [2016/11/16 11:30]
claudia
@@ Line 68: / Line 68: @@
-==== Results ====
+==== Results without atmosphere ====
-Example result:
+The following plots show the results obtained with MYSTIC. For all other models the patterns look the same.
-{{:intercomparisons:phase_c:c2_cubic_cloud:mystic_case6_noatm.png|Example result, cubic cloud - case6, no atmosphere}}
+{{:intercomparisons:phase_c:c2_cubic_cloud:c2_mystic_noatm.png|C2 without atmosphere, MYSTIC results}}
 ** General **
   * Generally we find a very good agreement between all Monte Carlo models, only for a few cases they do not agree within 2 standard deviations.
+  * The polarization patterns are the same in all models, also the pattern for V when variance reduction methods are applied
   * For SHDOM a quantitative comparison is difficult because it does not provide a standard deviation and systematic differences are expected (different treatment of cloud boundary. Smaller differences due to different solution method of VRTE).
-  * MSCART (backward mode) shows sytematic differences to the forward calculations, Wang Zhen already mentioned this. MYSTIC gives the same results in forward and backward mode.
+  * MSCART (backward mode) shows systematic differences to the forward calculations, Wang Zhen already mentioned this. MYSTIC gives the same results in forward and backward mode.
   * The agreed number of photons for this case is 49e9, this number has been used for 3DMCPOL, MSCART and MYSTIC. For SPARTA, 10e11 photons were used
+  * Circular polarization (Stokes component V) is very noisy in Monte Carlo results, especially for models without variance reduction.
-The following plots show the mean radiance (for each Stokes component), mean absolute difference with respect to MYSTIC (forward Monte Carlo), mean standard deviation, fraction of pixels which agree within 2 standard deviations. Only pixels with non-zero radiances are included into the statistics.
+The following plots show the mean radiance (for each Stokes component), mean absolute difference with respect to MYSTIC (forward Monte Carlo), mean standard deviation, fraction of pixels which agree within 2 standard deviations (2σ), please note the non-linear scale of the colorbar. Only pixels with non-zero radiances are included into the statistics.
 {{:intercomparisons:phase_c:c2_cubic_cloud:c2_statistics_1.png|Summary plots, statistics C2 without atmosphere}}
 {{:intercomparisons:phase_c:c2_cubic_cloud:c2_statistics_1.pdf|Summary plots, statistics C2 without atmosphere}}
-work in progress ...
+  * Stokes component I (upper row): The mean radiance (average over all non-zero pixels) is very similar for all models. The mean absolute difference is smaller than 1\% of the mean radiance. The mean differences are largest for SHDOM. Models without variance reduction (3DMCPOL, SPARTA) show larger differences than models with variance reduction (MSCART, MYSTIC-backward). Also the standard deviations are much smaller when variance reduction techniques are used (as expected). \\  The match fraction shows that all Monte Carlo models agree within 2σ for cases 5-9 (down-looking). The match fraction is between 0.9 and 0.95 for some up-looking cases 1-4, which might indicate a small bias between other models and MYSTIC. MYSTIC (forward and backward mode) agree perfectly.
+  * Stokes component Q (second row): The first column shows the mean absolute radiance (since Q can be positive or negative). The only visible difference in mean radiance is seen for case 5, here SHDOM is smaller than the Monte Carlo models, the difference is about 10%. \\ Mean standard deviations again are larger for models without variance reduction. The match fraction shows obvious systematic differences for mscart_bmc (all cases), mscart_fmc (cases 5 and 7) and SPARTA (case 6).
-  * Stokes component I (upper row): The mean radiance (average over all non-zero pixels) is very similar for all models. The mean absolute difference is smaller than 1\% of the mean radiance. The mean differences are largest for SHDOM. Models without variance reduction (3DMCPOL, SPARTA) show larger differences than models with variance reduction (MSCART, MYSTIC-backward). Also the standard deviations are much smaller when variance reduction techniques are used (as expected). \\  The match fraction shows that all Monte Carlo models agree within 2 <m>sigma<\m> for cases 5-9 (down-looking). The match fraction is between 0.9 and 0.95 for some up-looking cases 1-4, which indicates a small bias between other models and MYSTIC. MYSTIC (forward and backward mode) agree perfectly.
+  * Stokes component U (third row): Largest difference for case 7, mean difference between SHDOM and MYSTIC is about 5% of mean radiance. The match fraction shows obvious systematic differences for mscart_bmc (all cases), mscart_fmc (case 7).
-  * Stokes component Q (second row): The first column shows the mean absolute radiance (since Q can be positive or negative). The only visible difference in mean radiance is seen for case 5, here SHDOM is smaller than the Monte Carlo models, the difference is about 10%. \\ Mean standard deviations again are larger for models without variance reduction. The match fraction shows obvious sytematic differences for mscart_bmc (all cases), mscart_fmc (cases 5 and 7) and SPARTA (case 6).
+  * Stokes component V (bottom): Very noisy, without variance reduction (SPARTA, 3DMCPOL) noise is much larger than mean radiance. The match fraction shows systematic differences for mscart_bmc and mscart_fmc (all cases).
-  * Stokes component U (third row): Largest difference for case 7, mean difference between SHDOM and MYSTIC is about 5% of mean radiance. The match fraction shows obvious sytematic differences for mscart_bmc (all cases), mscart_fmc (case 7).
+These differences might be numerical because the mean radiance is very small (about 2e-6). Since the standard deviation is an order of magnitude larger than the radiance for SPARTA and 3DMCPOL, the results mostly match within 2σ, but this does not show whether the models really agree.
-  * Stokes component V (bottom): Very noisy, without variance reduction radiance has same order of magnitude as standard deviation.  The match fraction shows sytematic differences for mscart_bmc and mscart_fmc (all cases).
+  * Generally the standard deviation for SPARTA is below 3DMCPOL because for SPARTA more photons were used (10e11 vs. 49e9). MYSTIC and MSCART used 49e9 photons and variance reduction techniques which decrease the standard deviation approximately by almost one order of magnitude.
+==== Results with atmosphere ====
+The following plots show the results obtained with MYSTIC. For all other models the patterns look the same.
+{{:intercomparisons:phase_c:c2_cubic_cloud:c2_mystic_noatm.png|C2 without atmosphere, MYSTIC results}}
+Statistics for the cases with atmosphere
+{{:intercomparisons:phase_c:c2_cubic_cloud:c2_statistics_1.png|Summary plots, statistics C2 with atmosphere}}
 {{:intercomparisons:phase_c:c2_cubic_cloud:c2_statistics_1.pdf|Summary plots, statistics C2 with atmosphere}}
-==== Results without atmosphere ====
+==== Detailed plots for all models, no atmosphere ====
 ** Statistics plots **
@@ Line 144: / Line 152: @@
-==== Results with atmosphere ====
+==== Detailed plots for all models - with atmosphere ====
 ** Statistics plots **

International Polarized Radiative Transfer

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