cdf_lut: Aerosol CDF Look Up Table

In AlexCast/apsfs: Monte Carlo code for simulation of atmospheric Point Spread Functions and spatially-resolved Spherical Albedo Functions

Aerosol CDF Look Up Table

Description

Calculates a Look Up Table (LUT) for the aersol cumulative distribution function to be used with the Monte Carlo calculations.

Usage

cdf_lut(ph, xout, method = "fixed")

Arguments

ph	Phase function table at single wavelength.
xout	Angle points for calculation. See Details.
method	One of "fixed", "adaptative". See Details.

Details

This function calculates the cumulative distribution function of aerosol phase functions between 0 and pi. It can use a fixed integration grid based on xout (must be fine angular grid resolution!) or an adaptive integration (any xout) based on integrate. Regardless of the method used, a fine resolution is recommended to reduce bias on the PSF simulation. If xout is not specified, the defaault is to use 1000 log10 spaced values between 0 and pi. If xout is provided, it must include 0 and pi.

For the integration, a linear interpolation (approx) is used in log10 space for the aerosol phase function. Method 'fixed' uses fixed integration steps with quadrature rule.

Note that the convention in atmospheric optics is to have the PF not normalized by 4pi steradian, so it is unitless instead of 1/sr as in ocean optics. The integral to 1 is:

integral_0^2pi integral_0^pi (PF(theta, phi) / 4pi) * sin(theta) * dtheta * dphi = 1,

which in isotropic conditions (lack of azimuthal dependence) simplified to:

integral_0^pi (PF(theta) / 2) * sin(theta) * dtheta = 1

Due to small numerical errors, the phase functions are renormalized to 1 before returning.

Value

A numeric vector with the aerosol scattering CDF.

Examples

cdf_lut(continental_ph_6sv[, c(1, 8)])

AlexCast/apsfs documentation built on Feb. 1, 2024, 9:48 p.m.