Questions for other users and developers can be posted on the RTTOV Forum.
| Frequently Asked Questions: |
- Do I need to bother to upgrade my version of RTTOV v10.2 to RTTOV v11?
If you want any of the following the answer is yes (if you have v7, v8 or v9 there are more reasons):- Improved clear air transmittance simulations for all gases due to improved underlying spectroscopy from LBLRTMv12.2 and coefficient files now on 54L (in fact these coefficient files work with v10.2)
- Capability to simulate visible and near-IR channels
- Capability to apply correction for non-local thermodynamic equilibrium
- Capability to perform Principal Components calculations for cloudy as well as clear-sky profiles
- Capability to specify scattering parameters explicitly for IR aerosol and cloud simulations
- New parameterisation for ice cloud particles for IR scattering simulations
- Two new aerosol particle types: volcanic ash (derived from aircraft measurements of the Icelandic eruption in 2010) and an Asian dust type
- Improved microwave scattering code including the capability to supply hydrometeor profiles in units of kg/kg
- Improved sea-surface microwave emissivity model FASTEM-6 (v11.2 and later)
- Improved performance particularly in the direct and K models and the cloudy IR scattering code
- Improved performance of the IR emissivity atlas
- Capability to convert coefficients to HDF5 format (in addition to the existing ASCII and binary formats)
- Ability to run and visualise output of RTTOV via a graphical user interface (as of v11.2)
- Ability to specify units for input gas profiles (as of v11.3)
- Ability to run PC-RTTOV for any surface type (as of v11.3)
- Ability to call RTTOV from Python or C++ (as of v11.3)
- Can I compile the code in single precision to save space?
Yes the precision of the variables are defined by the src/main/parkind.F90 module. This file needs to be edited to change the precision using the JPRB variable. Note however that running the adjoint models (AD and K) in single precision can result in significant errors in the output. - I don't have an ozone or CO2, CO, N2O, or CH4 profile to
include in the state vector. What can I do?
You can either make sure you have a coefficient file which includes the above in the mixed gases which is the case for most coefficient files anyway or you can still use a coefficient file with minor gas coefficients and the reference profile supplied with the coefficients is used. You must take care to set the logical flags for example opts%rt_ir%co_data etc to false if you don't have a CO profile. If you don't the program assumes you are providing a valid profile and will fail if you don't. - My profile top is below the top level required by RTTOV v11, how
do I best extrapolate it for RTTOV?
If you use the internal interpolation routines of RTTOV v11 to take the user supplied levels and put them on the RTTOV coefficient file levels then this will be done for you though at a cost in CPU. By default profiles are extrapolated with constant value at the top of the atmosphere, but there is a new option "reg_limit_extrap" (as of v11.2) which extrapolates profiles by maintaining the relative position between the relevant training profile limits to the top of the atmosphere. See the user guide for more details on this.
If you don't want to use the internal interpolation and instead supply a profile on the coef levels then for gas concentrations it is best to use the reference profile for levels above the top input level. The reference profile values are available in the coef structure e.g. for water vapour coefs%coef%ref_prfl_mr(:,coefs%coef%fmv_gas_pos(gas_id_watervapour)) where gas_id_watervapour is available in the rttov_const.F90 module. For temperature one can extrapolate from the top level of the input profile using a representative lapse rate from standard atmospheres. - Why does compilation with the HDF5 library fail?
You must first edit the file build/Makefile.local to point to the location of your HDF5 installation and to include the relevant compiler and linker flags.
If you do not use the new compilation script (build/rttov_compile.sh) you must also regenerate the RTTOV Makefiles to include the HDF5 code:
$ cd src/
$ ../build/Makefile.PL RTTOV_HDF=1
You can then compile RTTOV as usual (see the user guide). - Why does the emissivity and/or BRDF atlas code cause compilation errors?
This code requires either the HDF5 library (recommended) or the netCDF library in order to compile. Make sure that you edit the file build/Makefile.local to point to the location of your HDF5 or netCDF installation before you build the code. - Why do some of the tests fail when I compile with certain compilers (e.g. ifort)?
You should increase the stack size before running the test scripts, for example by executing:
$ ulimit -s unlimited
For PC-RTTOV tests running the K model with NTHREADS > 1, you may need to increase the OpenMP stack size as well:
$ export OMP_STACKSIZE=1000M