This README_jpld_Apr2024.txt file was last updated on 8 Apr 2024.
Copyright 2024 California Institute of Technology. Government sponsorship 
acknowledged.

================================================================================
                                GENERAL INFORMATION
================================================================================
Title of Dataset: Global Ionospheric Maps for Research -- JPLD Data Product

Contact information:

	Olga Verkhoglyadova
	Jet Propulsion Laboratory, California Institute of Technology
	olga.verkhoglyadova@jpl.nasa.gov

	Xing Meng
	Jet Propulsion Laboratory, California Institute of Technology
        xing.meng@jpl.nasa.gov
                 
Funding sources and sponsorship:
This work was sponsored by and performed at the Jet Propulsion Laboratory, 
California Institute of Technology, under a contract with the NASA.


================================================================================
                                DATASET DESCRIPTION
================================================================================

Gobal Ionospheric Maps (GIMs) are global maps of ionospheric total electron
content (TEC), generated from measurements of globally distributed GNSS
receivers using techniques as described in references 1 and 2. There are 
several types of global TEC maps, generated with slightly different processing
techniques and having different temporal and spatial resolutions.

The JPLD data product is one type of global TEC map with 15-minute cadence on a
1 degree by 1 degree grid. The JPLD data product is generated based on daily
operational GIM processing for the Deep Space Network (DSN). These GIM DSN runs
are multi-shell runs based on the approach described in reference 2. As a
comparison, the JPLI and JPLG data products are generated from single-shell GIM
runs. The number of GNSS ground receivers used in the GIM DSN runs changed 
throughout the years:  
  ~98 stations prior to 2003/10/19
  ~200 stations from 2003/10/20 to 2018/12/09
  ~300 stations from 2018/12/10 to 2022/10/02
  >300 stations from 2022/10/03 to present.
In addition, GPS and GLONASS constellations were used in the GIM DSN processing 
from 1 January 2000 to 6 July 2021, and GPS and Galileo afterwards.

The jpld*.nc file format is in netCDF4. Each file contains multiple epochs for
a day. Each subfolder contains the jpld*nc files for a year. The files also
contain TEC data quality flag. Estimated gridded TEC data occasionally have
negative values, therefore we manually set the negative values to 0.1 TECU, and
the data quality flag indicates those artificially-reset TEC values. The dataset
is updated monthly to include jpld*nc files for the most recent month.


Note:
1. There is one missing day of data: 31 Oct 2003, doy 303.
2. Data for the following days cover from 00:00UT to 23:30UT only:
   6 - 9 Jan 2023, 11 Jan 2023, 13 - 15 Jan 2023, 17 - 18 Jan 2023, 22 Jan 2023.


References:
1. Mannucci, A. J., B. D. Wilson, D. N. Yuan, C. H. Ho, U. J. Lindqwister, and
T. F. Runge (1998), A global mapping technique for GPS-derived ionospheric total
electron content measurements, Radio Sci., 33(3), 565 582, doi:10.1029/97rs02707.
2. Mannucci, A. J., B. Iijima, L. Sparks, X. Pi, B. Wilson, and U. Lindqwister
(1999), Assessment of global TEC mapping using a three-dimensional electron
density model, Journal of Atmospheric and Solar-Terrestrial Physics, 61(16),
1227 1236, doi:10.1016/s1364-6826(99)00053-x.