Quickstart: Brightness Temperature

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Quickstart: Brightness Temperature#

In this notebook, we’ll simulate broadband brightness temperatures for various surface temperatures using pyRadtran.

import pyradtran  # Registers the .pyradtran xarray accessor
from pyradtran import Var
import matplotlib.pyplot as plt
import numpy as np
import xarray as xr
from pathlib import Path
import pandas as pd
import logging

logging.getLogger('pyradtran').setLevel(logging.CRITICAL)  # Suppress verbose solver output

config_path = Path('config/velox.yaml')

ds = xr.Dataset(
    coords={
        'time' : '2025-04-04T23:00:00',
        'latitude' : [78.925],
        'longitude' : [12.3747329],
        'altitude' : ('altitude', [0, 10, 100]),
    },
    data_vars={
        'surface_temperature' : [253.15, 263.15, 273.15, 283.15, 293.15],
        'albedo' : [0, 0.25, 0.5, 0.75, 1],
    }
)

ds_sim = ds.pyradtran.run(
    config_path=config_path,
    return_dataset=True,
    save_to_file=True,
    params={
        'sur_temperature': Var('surface_temperature'),
        'albedo': Var('albedo'),
        'output_quantity' : 'brightness',
    },
    show_progress=False,
)

print("\nSimulation complete!")
print(f"Dataset variables: {list(ds_sim.data_vars.keys())}")
print(f"Dataset coordinates: {list(ds_sim.coords.keys())}")
print(f"Dataset shape: {ds_sim.dims}")

Simulation complete!
Dataset variables: ['zout', 'lambda', 'eup', 'edn', 'edir']
Dataset coordinates: ['surface_temperature', 'albedo', 'latitude', 'longitude', 'altitude']
Dataset shape: FrozenMappingWarningOnValuesAccess({'surface_temperature': 5, 'albedo': 5, 'latitude': 1, 'longitude': 1, 'altitude': 3})

fig, ax = plt.subplots(1, 3, figsize=(12, 4), sharey=True)

ds_sim.eup.sel(altitude=0).plot(ax=ax[0], vmin=230, vmax=300)
ds_sim.eup.sel(altitude=10).plot(ax=ax[1], vmin=230, vmax=300)
ds_sim.eup.sel(altitude=100).plot(ax=ax[2], vmin=230, vmax=300)

ax[0].set_title('Surface (0 km)')
ax[1].set_title('10 km')
ax[2].set_title('100 km')

fig.suptitle(r'Simulated Brightness Temperature for varying Surface Temperature and Albedo (1-$\epsilon$)')
plt.tight_layout()
../_images/b9e3e9328aa2c3e9d77087c67bb2dc50894e1d68b1ad6723e2f04686024d0455.png

Key learning#

In libRadtran, surface emissivity is handled indirectly through albedo using the convention:

[ \epsilon = 1 - \text{albedo} ]

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