JURASSIC (Inverse radiance modeling)
JURASSIC2 (Jülich rapid spectral simulation code version 2) is a software package developed by IEK-7 for simulating spectra in the infrared. Such spectra are typically measured by limb and nadir sounders carried by satellites in Earth orbit, and by stratospheric aircraft or balloons. Using the JURASSIC2 forward model in combination with an inversion algorithm implemented in JUTIL (Jülich tomographic inversion library) allows to deduce atmospheric temperatures and trace gas compositions from the measured spectra.
The core of JURASSIC2 was originally created by Dr. Lars Hoffmann. At the heart of the C++ model is a radiative transport model based on the emissivity growth approximation and the Curtis-Godson approximation. These band models calculate reference tables in advance and are therefore up to 1000 times faster than more precise models based on a case-specific computation for individual spectral lines (line-by-line model). Thanks to a 3D ray tracing procedure, the model can be adapted to the viewing geometries of a variety of instruments. Recent work by Dr. Sabine Griessbach has added a scattering module for more accurate simulation of clouds. In addition, the model contains, mainly for reference calculations, a highly accurate line-by-line model. JURASSIC2 offers a fast analytical derivative based on algorithmic adjoints that were developed in cooperation with the STCE institute of RWTH Aachen. The full model has been exposed to the Python programming language, greatly facilitating its day-to-day use. For large-scale retrievals on the Jülich supercomputer JURECA , JURASSIC2 employs a hybrid OpenMP/MPI parallelization and can efficiently work on single large-scale tomographic retrievals with hundreds of threads.
JURASSIC2 is being employed in the evaluation of CRISTA satellite data, CRISTA-NF measurements acquired during the RECONCILE campaign, and GLORIA measurements. GLORIA is unique in the sense that it uses a tomographic measurement pattern, where the same volume of air is scanned from the surrounding under a large variety of directions. JURASSIC2 has been optimized to perform corresponding tomographic retrievals with a minimal amount of processing time and computer memory. For example, these tomographic methods were successfully used to reconstruct a 3-D mountain wave over Iceland measured during a POLSTRACC flight. JURASSIC2 is also used for studies regarding the AtmoSat project.