The Successive Orders of Scattering Source

The successive orders of scattering source is an implementation of the multiple scattering source using the successive orders of scattering method. It can be enabled with

import sasktran2 as sk

config = sk.Config()

config.multiple_scatter_source = sk.MultipleScatterSource.SuccessiveOrders

Advantages

• The only available multiple scattering source that fully accounts for sphericity of the atmosphere

Disadvantages

• Weighting function calculations are only approximate

• Can use a large amount of RAM for large, polarized, calculations

• May require sub-layering in optically thick areas of the atmosphere

Initialization Options

The successive orders method is an iterative method which repeatedly refines the solution. When the method is initialized with the single scatter source function, each iteration physically represents including an additional “order of scatter” into the solution. The number of these iterations can be configured with sasktran2.Config.num_successive_orders_iterations.

Alternatively, the successive orders method can be initialized with the source function calculated with a discrete ordinates solution. This has two advantages: the first is that fewer iterations are required to reach convergence, typically only 1–2 instead of sometimes 50; the second advantage is that the discrete ordinates method can provide a reasonable approximation for the weighting functions, whereas full weighting function calculations in a successive orders model are extremely computationally expensive. This option can be enabled with the sasktran2.Config.init_successive_orders_with_discrete_ordinates option. If it is set then all of the standard discrete ordinates options apply to the source used to initialize the solution.

Notes

• The succesive orders of scattering source is not fully linearized, which means that weighting functions returned back will only be approximate.

Relevant Configuration Options

sasktran2.Config.multiple_scatter_source	Sets which (if any) multiple scatter source is to be used inside the calculation.
sasktran2.Config.num_sza	The number of solar zenith angle discretizations to use when calculating the multiple scatter source.
sasktran2.Config.num_successive_orders_iterations	The number of iterations to perform when using the successive orders of scattering multiple scatter source.
sasktran2.Config.init_successive_orders_with_discrete_ordinates	If set to true, when using the successive orders source, it will be initialized with a source calculated with the discrete ordinates source instead of a single scattering source.
sasktran2.Config.num_stokes	Sets the number of Stokes parameters used in the calculation.