The State Vector

The state vector is the set of atmsopheric parameters that we are trying to retrieve. In skretrieval the default behaviour is to define the state vector entirely through configuration options, however it is also possible to override this behaviour for more complicated applications.

Specifying the State Vector Through Configuration

The main processing class, skretrieval.Retrieval, takes in an argument state_kwargs which is responsible for defining the state vector. An example of this parameter is

state_kwargs={
        "altitude_grid": np.arange(0, 70000, 1000),
        "absorbers": {
            "o3": {
                "prior_influence": 5e5,
                "tikh_factor": 1e-2,
                "log_space": False,
                "min_value": 0,
                "max_value": 1,
            },
            "no2: {
                "prior_influence": 5e5,
                "tikh_factor": 1e-2,
                "log_space": False,
                "min_value": 0,
                "max_value": 1,
            }
        },
        "aerosols": {
            "stratospheric_aerosol": {
                "type": "extinction_profile",
                "nominal_wavelength": 745,
                "retrieved_quantities": {
                    "extinction_per_m": {
                        "prior_influence": 1e0,
                        "tikh_factor": 1e-2,
                        "min_value": 0,
                        "max_value": 1e-3
                    },
                    "median_radius": {
                        "prior_influence": 1e2,
                        "tikh_factor": 1e-4,
                        "min_value": 10,
                        "max_value": 900
                    }
                },
                "prior": {
                    "extinction_per_m": {"type": "testing"},
                    "median_radius": {"type": "constant", "value": 80}
                }
            }
        },
        "surface": {
            "lambertian_albedo": {
                "prior_influence": 0,
                "tikh_factor": 1e-2,
                "log_space": False,
                "wavelengths": np.array([280, 360]),
                "initial_value": 0.5,
            }
        },
        }

skretrieval provides default methods to construct the state vector for absorbers, aerosols, and surface parameters.

Defining Your own State Vector Elements

If the default skretrieval methods to construct the state vector are not sufficient, you can manually supply your own. This is done through the decorator method,

import skretrieval as skr

@skr.Retrieval.register_state("category", "name")
def state_vector_element(self, name: str, native_alt_grid: np.array, cfg: dict):
    # calculate state vector element here
    sv_ele = ...

    return sv_ele

here “category” should be replaced by one of [“absorbers”, “aerosols”, “surface”, “other”], and “name” will be the name of the state vector element in the configuration. For example, we could register a state vector element for SO2 absorption through

@skr.Retrieval.register_state("absorbers", "so2")
def state_vector_element(self, name: str, native_alt_grid: np.array, cfg: dict):
    # calculate state vector element here
    sv_ele = ...

    return sv_ele

When we construct state_kwargs we would then add a so2 section under absorbers, and any information added there will be passed through to the state_vector_element function above through the cfg parameter.