GPS Satellite Tracker is and android app that tracks the position of GPS Satellites(PRN, SNR, Elevation and Azimuth) around you that are used to get your current location. It uses the gps $GPGSV NMEA data to determine the position of GPS satellites.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data are transmitted in a "sentence" from one "talker" to multiple "listeners" at a time.
Example of $GPGSC sentence from https://www.gpsinformation.org/dale/nmea.htm:
$GPGSV,2,1,04,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75 Where: GSV Satellites in view 2 Number of sentences for full data 1 sentence 1 of 3 04 Number of satellites in view 01 Satellite PRN number 40 Elevation, degrees 083 Azimuth, degrees 46 SNR - higher is better *75 the checksum data, always begins with *