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**What is OASIM? **
The OASIM (Optical Absorption and Scattering of Irradiance Model) is a computational model designed to simulate the interaction of sunlight with ocean water. It is typically used in oceanographic and atmospheric research to predict and understand the behavior of light in the ocean, including absorption, scattering, and irradiance at different depths. The model has applications in climate studies, marine biology, and remote sensing.
Key Features of OASIM: Light Propagation Simulation:
Models how solar radiation penetrates through the ocean surface and interacts with water molecules, phytoplankton, dissolved organic matter, and suspended particles. Wavelength Dependence:
Accounts for variations in light absorption and scattering properties across different wavelengths of sunlight. Ocean-Atmosphere Interaction:
Incorporates interactions between the ocean surface and atmospheric factors like cloud cover, aerosols, and gases.
Inputs: Solar irradiance (incoming sunlight) Water composition (chlorophyll concentration, dissolved organic matter, etc.) Atmospheric properties (aerosol optical thickness, humidity, etc.) Wind speed (affecting surface waves and light reflection/refraction).
Outputs: Downwelling and upwelling irradiance profiles.
Irradiance Pathways in OASIM
Ed is direct downwelling irradiance, Es is diffuse downwelling. ρ surface reflectance, Eu is diffuse upwelling irradiance, and Lw N is normalized water-leaving radiance. All irradiances and radiances are spectrally resolved at 25 nm for Ed , Es , and Eu . and 1 nm for Lw N.
Optical Properties of Ocean Constituents
Optical Properties of Ocean Constituents Included in OASIM as look up tables with 25 nm resolution
Structure of OASIM
all the scripts for running OASIM model are located at
https://github.com/JCSDA-internal/oasim/blob/develop/src/oasim/
**oasim_mod.f90 ** is the main function
**sfcirr_mod.f90 ** is the sub function to calculate Spectral irradiance just above surface
glight_mod.f90 derives the Spectral irradiance in the water column
rlwn_mod.f90 was not in the initial package received from GMAO, and was added by me to derive the water leaving radiance
OASIM Operator in UFO
you can find the OASIM operator in UFO here:
https://github.com/JCSDA-internal/ufo/tree/develop/src/ufo/operators/oasim
and the test for this operator here:
for testing this operator we needed to create a geoval files with the OASIM inputs. We created this geoval file "Data/ufo/testinput_tier_1/pace_radiance_geovals_2019032112.nc" using monthly averaged MERRA, MODAER and NOBM data,
we derived different variables from these files as following:
-- MERRA:
SLP : Sea level pressure (hPa)
WSPD : Surface_wind_speed (m s-1)
OZONE : Ozone thickness (dobson units)
WVAPOR : Water vapor (cm)
RH : Relative humidity (percent)
COV : Cloud cover (percent)
CLWP : Cloud liquid water path (dimensionless)
-- MODAER:
TA_IN : Aerosol optical thickness (dimensionless) ASYM : Asymmetry parameter (dimensionless) WA_IN : Single scattering albedo (dimensionless)
-- NOBM:
DH : Layer thickness (m)
CDET : Carbon/nitrogen_detritus_concentration
PIC : Particulate inorganic carbon (ugC l-1)
CDC : Colored dissolved organic carbon (uM)
DIATOM : Diatom concentration (mg m-3)
CHLORO : chlorophyte_concentration (mg m-3)
CYANO : Cyano-bacteria concentration (mg m-3)
COCCO : Coccolithophore concentration (mg m-3)
DINO : Dinoflagellate concentration (mg m-3)
PHAEO : Phaeocystis concentration (mg m-3)
OASIM in SKYLAB
we successfully ran OASIM hofx in SKLYAB using the https://github.com/JCSDA-internal/skylab/blob/develop/experiments/mom6-hofx3d-025deg.yaml and coupled-gfs-mom6-hofx.yaml experiments, for these experiments Ocean data is coming from MOM6, biochemistry data from NOBM and some atmospheric variables from GFS. this plot shows the OASIM coupled hofx in Skylab for Channel 10 of modis-aqua, Surface pressure and wind speed from gfs other atmospheric variables needs to be derived from gfs
OASIM in coupling repo
We added a test for coupled OASIM hofx in coupling repo here:
this was tested using the Data/obs/testinput_tier_1/modis_aqua_oc_obs_20201215_m.nc data, here We derived aerosol optical thickness by calling CRTM_AOD inside oasim Tested for MODIS 10 Channels Right now, Surface pressure and wind speed coming directly from gfs, and aerosol optical thickness derived from gfs_aod, the following variables are still needed to be derived from gfs
ASYM : Asymmetry parameter (dimensionless)
WA_IN : Single scattering albedo (dimensionless)
OZONE : Ozone thickness (dobson units)
WVAPOR : Water vapor (cm)
RH : Relative humidity (percent)
COV : Cloud cover (percent)
CLWP : Cloud liquid water path (dimensionless)
this plot shows the obs-hofx in coupling repo for Channel 10 of modis-aqua, Surface pressure and wind speed from gfs and aerosol optical thickness derived from gfs_aod
