Added some docs regarding the PostgreSQL database and the pre-defined virtual sensors.

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>

HISTORY.rst

@@ -2,6 +2,12 @@
 History
 =======
 
+0.19.4 (coming soon)
+--------------------
+
+* Added some docs regarding the PostgreSQL database and the pre-defined virtual sensors.
+
+
 0.19.3 (2020-12-03)
 -------------------
 

docs/infrastructure/postgresql_db.rst

 PostgreSQL metadata database
 ============================
 
-* TODO
+GeoMultiSens interacts with a PostgreSQL database that contains all the satellite image metadata for all datasets that
+can be processed. Apart from that, it contains system-wide configuration parameters and some statistical data.
+
+The database consists of the following tables:
+
+.. csv-table::
+   :header: "Table", "Description"
+   :widths: 10, 30
+
+   config, system-wide configuration parameters for GeoMultiSens
+   datasets, records of datasets supported by GeoMultiSens
+   footprints_sentinel2_granules, spatial footprints of Sentinel-2 granules
+   jobs, processing and analysis jobs and their attributes
+   mgrs_tiles, spatial footprints of MGRS (military grid reference system) tiles
+   mgrs_tiles_proc, records of already processed MGRS tiles
+   satellites, records of satellites supported by GeoMultiSens
+   scenes, records of satellite image metadata
+   scenes_proc, records of already processed satellite images
+   scenes_sentinel2, separate table for Sentinel-2 metadata
+   sensors, records of sensors supported by GeoMultiSens
+   spatial_ref_sys, records regarding the spatial reference system
+   stats_mem_usage_homo, memory usage statistics for different job configurations
+   subsystems, records of subsystems supported by GeoMultiSens
+   virtual_sensors, records of target sensors of the spectral and spatial homogenization
+

docs/usage/create_new_jobs.rst

@@ -7,8 +7,24 @@ There are multiple ways to create new jobs depending on what you have. The secti
 
 .. note::
 
-    Only those datasets that were correctly added to the local GeoMultiSens data storage before can be used to create a
-    new GeoMultiSens preprocessing job (see :ref:`ref__add_new_data_to_the_database`).
+    * Only those datasets that were correctly added to the local GeoMultiSens data storage before can be used to create
+      a new GeoMultiSens preprocessing job (see :ref:`ref__add_new_data_to_the_database`).
+
+    * You need to set the parameter `virtual_sensor_id` when creating a new processing job
+      to define which target sensor is used for spatial and and spectral homogenization.
+      Here is an overview of pre-defined target sensors:
+
+      .. csv-table::
+          :header: "virtual_sensor_id", "target sensor escription"
+          :widths: 4, 10
+
+          1, Landsat-8
+          10, Sentinel-2A 10m
+          11, Sentinel-2A 20m
+          12, Sentinel-2A 60m
+          19, Landsat-5
+          20, Landsat-7
+          21, Sentinel-2A spectral bands at Landsat pixel grid
 
 
 Create a job from a list of filenames