Effects of Polarization

Official code comparison Web site of the MODIS atmospheric correction group

1. The effects of light polarization for different types of an atmosphere are demonstrated  here through the comparison of simulations produced by the 6SV1 code in vector and scalar modes. The comparison shows that ignoring the effects of polarization leads to large errors in calculated TOA reflectances. The maximum ((vector-scalar)/vector)*100% error is as large as 6.0% for an ordinary mixed (molecular + aerosol) atmosphere. Therefore, the accounting for polarization is extremely important for atmospheric correction of remotely sensed data, especially those measured over dark targets, such as dark dense vegetation canopy or ocean surface.

2. In addition to the effects of polarization, we also estimated the influence of errors in TOA reflectance values produced by the codes on the accuracy of aerosol optical thickness and surface reflectance retrievals. The term "error" here implies all differences originating from error sources associated with a particular code. The estimation method is explained on slide 26 of the Project Presentation.


• Effects of polarization for a molecular atmosphere

Figure 1. Effects of polarization for a pure molecular atmosphere. SZA = {0.0-; 10.0-; 23.07-; 45.0-; 58.67-; 75.0-}, VZA = {0.0- - 79.0-}, AZ = {0.0-; 90.0-; 180.0-}, τ= {0.1; 0.3445}, ρ= 0.0.


• Effects of polarization for a mixed (molecular + aerosol) atmosphere

Figure 3. Effects of polarization for a mixed atmosphere. SZA = {0.0-; 11.48-; 23.07-; 32.86-; 58.67-}, VZA = {0.0- - 79.0-}, AZ = {0.0-; 90.0-; 180.0-},τaer = 0.728, τmol = 0.177 for λ = 470 nm and τmol = 0.042 for λ = 670 nm, ρ = 0.0.  The aerosol constituent is represented by "biomass burning smoke".


• Influence on optical thickness retrieval

Figure 5. Errors on ρsurf retrievals obtained for the same cases of a mixed atmosphere as in Fig. 4, but bounded by a Lambertian surface with the reflectance of 0.05. The aerosol constituent is represented by the AF model. Each error value is averaged over three azimuths, AZ = {0.0-; 90.0-; 180.0-}.

Results (UI)Results (AF)Results (AS)

• Effects of polarization for an aerosol atmosphere

Figure 2a. The average volume size distribution of particles for the "biomass burning smoke" aerosol model.

Figure 2b. Effects of polarization for a pure aerosol atmosphere (simulated by "biomass burning smoke"). SZA = {0.0-; 11.48-; 23.07-; 32.86-; 58.67-}, VZA = {0.0- - 79.0-}, AZ = {0.0-; 90.0-; 180.0-},τ = 0.728 (hazy conditions),λ = {470; 670} nm, ρ = 0.0.


• Influence on aerosol optical thickness retrieval

Figure 4. Errors on τaer retrievals obtained for 6 cases of a mixed atmosphere bounded by black surface. The aerosol constituent is represented by the AF model. Each error value is averaged over three azimuths, AZ = {0.0-; 90.0-; 180.0-}.

Results (UI)Results (AF)Results (AS)


Note: For more information on the effects of polarization, please check our 6SV validation papers. More information on the analysis of retrievals can be obtained by request from the MODIS atmospheric correction group.