How GPS Works: The Science Behind Satellite-Based Positioning
- Anvita Shrivastava
- Aug 10
- 6 min read
Updated: Aug 11
Global Positioning System, or GPS, is the essential technology behind the use of drones, UAV navigation, aerial mapping, surveying, and geospatial data collection. GPS is the key technology in the operation of UAVs. It helps to track their movement and navigate them to specific locations.
How does GPS really function?
GPS works by sending signals that come from satellites high above the Earth. The GPS receiver mounted on the drone or other devices tracks the signals and, based on this input, the GPS receiver is able to receive and process the signals coming from various satellites and detect the location. GPS solutions can also be enhanced with various technologies such as GNSS, RTK, and PPK.
What Is GPS?
GPS is the abbreviation for Global Positioning System, a satellite-based navigation system managed by the United States government.
GPS belongs to the larger Global Navigation Satellite System (GNSS) family of satellite navigation systems. Other systems that belong to this family include:
GPS (USA)
Galileo (EU)
GLONASS (Russia)
BeiDou (China)
Contemporary drone navigation systems can utilize signals from various GNSS systems, rather than relying solely on GPS. By doing this, the availability of satellites is increased, thus enhancing the reliability of the positioning process.
In UAV applications, GNSS positioning is beneficial for:
Navigation of the drone
Stabilization of the flight
Execution of waypoint missions
Functionality of return to home
Implementation of geo-fencing
Aerial mapping
Conducting surveys
Precision farming
Inspection of the infrastructure
LiDAR data collection
How GPS Satellites Determine Your Position
GPS satellites function at an altitude of around 20,200 kilometers (12,550 miles) above the planet’s surface. All satellites transmit signals that bear specific details and information, e.g.:
An accurate time of transmission
Identification of the satellite
Information regarding the orbit
Details of the timekeeping ability of the satellite
Data critical in navigation
A GPS receiver on a drone utilizes the information provided to determine the position of the satellites at the moment of the transmission of the signals.
Since the signals travel at a speed equal to the speed of light, measuring their time of travel gives an idea of the distance separating a satellite and a receiver.
The basic formula used here is:
Distance = the travel time of the signal/ speed of light.
Even a minor mistake in determining the time of transmission may cause significant navigation error; therefore, GPS satellites make use of very precise atomic timekeepers.
Why Does a Drone Need GPS?
The significance of GPS technology lies in the fact that it plays a vital role in ensuring successful operations of UAVs.
The flight controller of a UAV is dependent on GNSS technology to accomplish different tasks.
Position Maintenance
GNSS technology allows a UAV to keep its location close to its geographical position even when the pilot takes his hands off the sticks.
Waypoint Navigation
In the course of mapping and survey missions, it is compulsory for UAVs to comply with predetermined flight paths that have been previously configured with the help of GNSS data.
Return to Base
Some UAVs employ GNSS technology in order to find their launching pad and fly back to it with an activated return function.
Automated Missions
UAV technologies provide professionals with numerous opportunities to enlist GNSS technology for planning automated flights and repeating the flights.
Geofencing
Geofencing systems employ GNSS technology to identify and monitor the areas where the UAVs are not allowed to fly.
Mapping and Surveying
Detailed GNSS technology helps connect various aerial photographs and sensor readings to the actual geographical coordinates.
GPS Signals and Drone Receivers
A GNSS receiver in a drone interprets signals sent from satellites.
GPS utilizes several frequency ranges, all of which fall under:
L1
L2
L5
Up-to-date commercial GPS receivers are capable of utilizing various frequency bands and numerous satellite systems.
Multiband positioning is of utmost relevance in the context of high-precision survey applications, as it assists in correcting certain signal errors, such as ionospheric ones.
The GNSS receiver activates satellites through their own unique pseudo-random noise (PRN) codes, then follows them to obtain the navigational data necessary to calculate satellite locations and signal propagation time.
What Is Pseudorange?
Pseudorange is an important measurement in GPS.
Pseudorange is calculated based on the travel time of the signal from the satellite to the receiver.
The term pseudo implies that the measurement is influenced not only by the physical distance.
Some causes of error are as follows:
Receiver clock bias
Satellite clock errors
Ionospheric delay
Tropospheric delay
Multipath
Satellite orbit errors
Receiver noise
Modern GNSS methods use further measurements and correction models to minimize the errors.
GPS Errors That Affect Drone Positioning
Various factors can cause inaccuracies with GPS positioning.
Atmospheric Interference
The ionosphere and troposphere influence the speed at which the GPS signal travels and its reception.
To minimize the impact of these interferences, dual-frequency GNSS receivers are helpful.
Multipath Interference
The signal might bounce back off buildings and other surfaces before reaching the receiver.
Such bounces can lead to errors in positioning.
Satellite Positioning
The satellites that are visible and positioned up in the sky have a bearing on the accuracy of GPS.
In general, the more spread out the visible satellites are, the better the GPS accuracy.
Position of the Satellite
The errors in determining the position of the satellites also throw off the positioning of drones.
Time Error
GPS is all about timing, and even the smallest of errors in this regard can create inaccurate distance readings.
GPS and Drone Photogrammetry
The role of GNSS in Drone Photogrammetry is major.
In a mapping mission, the UAV collects several hundred or even thousands of pictures that significantly overlap with one another. Every picture has a certain position and orientation of the drone.
Photogrammetry software employs these images and position data to recreate the studied territory.
The workflow is typically: GNSS positioning → UAV flight → Image capture → Photogrammetric processing → Georeferencing → 3D reconstruction → GIS analyses.
The result can be any of the following: Orthomosaic maps, digital elevation models (DEMs), digital terrain models (DTMs), digital surface models (DSMs), 3D mesh, point cloud, contour map, volumetric computations.
With precise GNSS positioning, a reliable geographic reference for the datasets can be obtained.
GPS vs. GNSS for UAV Applications
The terms GPS and GNSS should not be treated as synonymous.
GPS is specifically the detection system of the United States.
GNSS is a common term for various kinds of satellite detection systems.
Some advanced civilian drones may operate at the same time using a handful of satellite systems.
For example;
GPS + Galileo + GLONASS + BeiDou = Multi-GNSS position
The system's ability to utilize multiple detection systems at once means that more satellites can be employed and the performance improved in the difficult conditions of use.
The Future of GPS-Based Drone Navigation
UAV positioning will not only rely on GPS in the future.
Presently, modern drones combine various technologies and sensors:
GNSS + RTK/PPK + IMU + LiDAR + Computer Vision + AI + HD Maps
The term for this is sensor fusion.
Sensor fusion enables the drone to remain situated in a particular location as long as a satellite signal is present.
For example, while GNSS is responsible for global positioning, visual odometry, cameras, LiDAR, and inertial sensors can give supplementary details regarding the surrounding environment of the drone.
This is useful for:
Autonomous UAVs
Drone delivery
Indoor drone navigation
Urban drone operations
BVLOS operations
Infrastructure inspection
Precision mapping
Robotics
The more autonomous UAV technology progresses, the greater the demand becomes for precise positioning.
In addition to being a navigation tool on mobile devices, GPS is an advanced positional technology that combines satellite timing, orbital data, radio signals, and trilateration.
With respect to UAV operations, GPS and GNSS provide an essential basis for navigation, flight route missions, return-to-base capabilities, aerial surveying, and other autonomous flying features.
Where ultra-high precision mapping is needed, RTK and PPK technology help in achieving centimeter-level positioning accuracy for drones. These technologies, integrated with IMUs, LiDAR, computer vision, and AI, are contributing to the emergence of more autonomous and highly accurate UAVs.
As agriculturists, surveyors, construction workers, miners, inspectors, and geospatial mappers increasingly adopt drones, the knowledge of GPS functioning and advanced GNSS technology for higher precision becomes paramount.
For more information or any GPS questions, please don't hesitate to contact us at:
Email:
USA (HQ): (720) 702–4849
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