.. _lambda-sec-ttt:

Travel-Time Tables
==================

Predictions of phase arrival times are required for :ref:`backprojection <lambda-sec-methods-backproj>`
and for indicating theoretical arrival times. They are either provided as

* Travel-time tables for :cite:t:`locsat` are located in
  :file:`@DATADIR@/locsat/tables`. One
  file per considered model and phase type must exist in that directory
  named as :file:`[model].[phase]`.
* Velocity models for libtau in :file:`@DATADIR@/ttt`. The provided models are
  ak135 and iasp91. The model files should not be changed.

General parameters can be adjusted by global module configuration.

* Example for LOCSAT and libtau adding the model *iasp91_scanloc* which ships
  the :cite:t:`scanloc` package: ::

     ttt.LOCSAT.tables = iasp91,iasp91_scanloc
     ttt.libtau.tables = iasp91,ak135

For viewing the phases in :program:`scolv`, they must be added to the
configuration in :file:`scolv.cfg`, e.g.: ::

   picker.showPhases = P,Pn,Pg,pP,sP,S,Sg,Iw


Seismic phases
--------------

Existing seismic travel-times for :cite:t:`LOCSAT` or velocity models for
libtau can be used. New models and files for phases can be added for LOCSAT.


Infrasound phases
-----------------

LAMBDA ships with travel-time tables predicting the arrival of infrasound phases
for :cite:t:`locsat`.
The table files are located in :file:`@DATADIR@/locsat/tables`.
The phase names are derived from :cite:t:`brown-2002`.

.. csv-table::
   :header: "Phase name", "Table file", "Meaning"
   :widths: 15,15,70

   ILm, , Lambda wave arrival
   Is, iasp91.Is, Stratospheric arrival
   Isx,, Stratospheric coda phase arrival
   It, iasp91.It, Thermospheric arrival
   Itx,, Thermospheric coda phase arrival
   Iw, iasp91.Iw, Tropospheric level wind generated arrival
   Iwx,, Tropospheric level wind generated coda phase arrival
   N, , Tropospheric level wind generated arrival

These travel-time tables are only rough estimates of the arrival times of sound waves
at the given distances and source depth / elevation. Currently, we
recommend to use only the backazimuth from infrasound detection for event location.