Online calculator of atmospheric 3D radiative transfer

Figure 1: User interface for setting up simulations using the online calculator. Figure 2: A sample result from the online calculator. The image shows the calculated reflectance (that is, normalized radiance) field that an observer looking straight down at a cumulus cloud field would see. The sun shines from the left, which results in bright areas in the left side of clouds, and in dark areas both in the right side of clouds and in shadows on the ground.

The Intercomparison of 3D Radiation Codes (I3RC) project sponsored the development of a community model of 3D radiative transfer. This model has now been expanded to create the first online calculator of atmospheric 3D radiative processes. The calculator offers researchers, students, and the public a simple way to perform quick simulations to test new hypotheses and to explore 3D radiative processes. For cloud fields specified by users, the calculator can yield the spatial distribution and scene average value of radiances, fluxes, and absorption at selected visible and near-infrared wavelengths. To help better understand the 3D nature of radiative processes, the calculator can also use an approximation widely used in remote sensing and in dynamical models, and perform 1D calculations for each atmospheric column without considering interactions between columns. Since its public release in January 2012, 100 unique visitors from 15 countries have tried the calculator. The online calculator and the source code of the I3RC community model of 3D radiative transfer are available at http://i3rc.gsfc.nasa.gov/i3rcmodel .

Figure 1 shows the simple online interface for setting up calculations. Users can set simulation parameters such as wavelength or solar and view directions using drop-down menus. 3D cloud structure is specified in a text file users need to upload, with the file format following the convention of popular 3D radiation models.

Figure 2 shows a sample result for one of the test cases that were used in the I3RC project for evaluating various simulation techniques. The figure shows the top view of a cumulus cloud field generated through offline dynamical simulations. Colors indicate reflectances at a near-infrared wavelength often used in satellite measurements of cloud particle size and phase. The fact that simulation noise is fairly small reveals that the calculator can provide reliable results through its quick simulations limited to 5 minutes.