Planets Starter Pack

This archive contains datasets for performing calculations with the htrdr-planets program. No-frills shell scripts are also provided that run htrdr-planets on this data. Command-line arguments are defined using variables for easy reading. In fact, these scripts are examples that are good starting points for studying how to run htrdr-planets. Users are encouraged to edit and extend them.

To run computations, assuming htrdr-planets is installed and registered in the current shell, one can simply execute the desired script. Computed images can be converted into regular PPM images which can then be displayed with a normal image viewer. For instance, for the Titan test case:

sh htrdr-Planets-Starter-Pack-0.1.0/draw_titan.sh
htpp -i exposure=1e-2 -o titan.ppm titan_1280x960x256.txt

Content

Titan

The titan directory contains the following data describing Titan:

• a sphere of radius 2574.73 km, discretized into 128,880 triangles defined using 64,621 nodes. The surface material uses a reflectivity of 20% in the [0.30, 0.90] µm range, and 0% (blackbody) for wavelengths in the [0.90, 5.1225] µm.
• a gas mixture, whose spectral properties (absorption and Rayleigh scattering coefficients) are provided for 1,064,672 nodes that define 1,552,320 tetrahedra, for 70 spectral intervals over the [0.3, 1250] µm spectral range.
• two aerosol modes (“haze” and “cloud”) whose spectral properties (absorption and scattering coefficient, as well as the asymetry parameter for the Henyey-Greenstein phase function) are provided over the same geometric and spectral grids as for the gas mixture.

Random01

Images rendered by htrdr-planets from the random01 dataset. The infrared image (bottom) is a map of brightness temperature, in Kelvins. Cold zones (in altitude) or highly reflective (i.e. weakly emitting) zones are made visible because of their lower specific intensity.

The random01 directory contains the following data, produced by the planet_generator program:

• a planet of base radius 6371 km, but augmented with a 3D orography: a number of altitude perturbations are randomly generated, each adding a “bump” (positive or negative) in the geometry obtained at the previous step. Then altitudes are rescaled to match a given maximum (in this case, 8 km) and a final remesh is applied so that the triangles neatly follow a number of level curves. The present triangular surface grid uses 490,420 nodes that define 882,094 triangles. Each altitude zone is then attributed a given material. Each material comes with its spectral reflectivity, over the visible and infrared spectral ranges. A temperature is computed for each triangular face as a function of its altitude, using the terrestrial adiabatic lapse rate.
• a gas mixture whose spectral properties (absorption and Rayleigh scattering coefficients) are provided for 814,666 nodes that define 4,838,400 tetrahedra, for 110 spectral intervals over the [0.2, 100] µm spectral range. The k-distribution dataset (both for the visible and infrared range) at each node has been interpolated as a function of its latitude, from the known k-distribution datasets for five standard atmospheric profiles of the terrestrial atmosphere.

sun_intensity_lite.bin

The description file for the specific intensity of the external source contains two columns: the value of the wavelength in nanometers, and the value of the specific intensity in W/m²/sr/nm.

Please note that the values of the specific intensity are for a position over the sphere that represents the source (i.e. for an emission location). For instance, in the case of the Sun: we know the solar flux that reaches the terrestrial orbit is approximately 1368.7 W/m². Now imagine that the original data is made of values of the solar flux for the orbit of the Earth in W/m²/nm, for a number of wavelengths, and that the spectral integral of this signal is 1368.7 W/m². In order to obtain the values of the specific intensity of the Sun, for each wavelength, these values of flux would have to be multiplied by 1 A.U. in km / radius of the Sun in km / pi, in order to compute the specific intensity of the Sun when radiation is emitted at any position over the sphere that represents the Sun. The spectral integral of this specific intensity signal, that has to be written in the specific intensity file, would be 20,156,476.20 W/m²/sr.

Copyright notice

Copyright © 2023, 2024 Centre National de la Recherche Scientifique
Copyright © 2023, 2024 Institut Pierre-Simon Laplace
Copyright © 2023, 2024 Institut de Physique du Globe de Paris
Copyright © 2023, 2024 |Méso|Star> (contact@meso-star.com)
Copyright © 2023, 2024 Observatoire de Paris
Copyright © 2023, 2024 Université de Reims Champagne-Ardenne
Copyright © 2023, 2024 Université de Versaille Saint-Quentin
Copyright © 2023, 2024 Université Paul Sabatier

License

htrdr: Planets Starter Pack is released under the GPLv3+ license: GNU GPL version 3 or later. You can freely study, modify or extend it. You are also welcome to redistribute it under certain conditions; refer to the license for details.