Thank you for joining us for the second part in our Guide to Wildlife Tracking Technology. Today we discuss the use and role of GNSS Cellular Collars. Enjoy!
GNSS (GPS) Cellular
The first automated tracking
GNSS Cellular collars, also known as GPS GSM or GPS Cellular collars, offer fully remote automated data collection and delivery. Location data is autonomously collected by the tracking device and delivered to the user via cellular networks and the Internet. The technologies involved have been around for a very long time and the physical size of the tracking devices are getting ever smaller. One of the greatest challenges with this technology option remains the poor reach of cellular networks into rural areas. It is a cost-effective option for the collection of location data over time as it requires no manual effort from the user. VHF transmitters are often included with GNSS Cellular devices as an option to track the animal when visual monitoring is needed.
How do GNSS Cellular tracking devices work?
The Global Positioning System (GPS) was the first commercially available Global Navigation Satellite System (GNSS) available – and is still the most widely used. There are more systems in operation such as Galileo, BeiDou and GLONASS. Modern GNSS receiver modules are capable of using multiple of these systems to improve performance in acquiring locations.
GNSS cellular tracking devices combine a GNSS receiver with cellular module and some memory for data storage. The GNSS receiver module acquires location coordinates and time from GNSS systems such as GPS. Once a location is acquired the tracking device stores it in memory with the time and date. Collected data is sent to a computing platform on the Internet via a cellular network. The platform could make the data available to the user via email, an Application Programming Interface (API) or via a web portal.
Typically GNSS Cellular tracking devices are configured to acquire locations on a set schedule and to attempt to upload data on a second schedule. If the network coverage does not permit uploading, these devices often have the ability to store the data until there is an opportunity to upload the data in a subsequent scheduled upload.
How do you track an animal with a GNSS Cellular device?
Data points from GNSS Cellular tracking devices devices are automatically uploaded from the device via the cellular networks to a service provider’s platform on the Internet. Generally the user of the system does not need to perform any field work to get access to the data. The data is either delivered directly via email to the user or it may be accessed via an application that provides options to visualise the data on maps or download the data for analysis or use in third party applications.
Because geographic coordinates are acquired and uploaded on a schedule, the user will only get the latest location at the time of a successful upload. The acquired coordinates can be viewed on a map or put into a handheld GPS receiver to guide the user to the point. If a VHF transmitter is included in the tracking device, the last received coordinates is a good place to start searching for VHF signal if physical observation is required.
The maximum accuracy of a civilian GNSS receiver is about 2 m. In practice however the accuracy of acquired locations are typically 5 m to 10 m in good conditions. Each acquired location has a varying degree of accuracy depending on where the satellites used for the acquisition are located. The highest accuracy can be achieved if the GNSS receiver’s antenna has an unobstructed vantage point to the full sky. In these ideal conditions multiple satellites from different segments of the sky are used in calculating the location – providing quick and accurate results. If the GNSS antenna is partially obstructed by terrain or vegetation, or if it is oriented away from the open sky, the GNSS receiver will take longer to acquire a location and the accuracy of that location will be reduced because the satellites used may be within the same area of sky, which reduces the ability to get an accurate ‘fix’. Good GNSS devices measure the accuracy of each location and provide a horizontal dilution of precision (HDOP) which gives an indication of the possible error on the acquired location.
GNSS Cellular device power consumption
GNSS Cellular devices can be very power efficient depending on the brand and how they are configured. There are two primary elements that contribute to to battery draw namely the GNSS receiver and the Cellular module.
GNSS receiver power consumption
The amount of battery power consumed by a GNSS receiver whilst acquiring satellite data and the determination of location depends on the brand and components used and whether an active or passive antenna is connected. Active antennas compensate for signal loss in the feeding cable between the GNSS receiver and the antenna element. Active antennas are generally not required where short antenna cables are used – but this is dependent on the design of the tracking device or collar.
Most GNSS receivers store satellite ephemeris data from the GNSS satellites so that when they start up again within a certain period of time (two hours or less), some of the data is still valid and the time to get a location – known as Time to Fix (TTF) – is shorter than it would be when starting with no data – known as Time to First Fix (TTFF). Every two hours or so the receiver needs to replenish its ephemeris data to reduce any future TTF. When a GNSS device is started up in good sky view within a minute of its last ‘fix’, it could get a new ‘fix’ in a TTF of 1 second. This is called a ‘hot start’. When starting up 5 minutes to 2 hours after refreshing its ephemeris data, a GNSS receiver can ‘fix’ in a TTF of 5 to 15 seconds – known as a ‘warm start’. When starting up with no ephemeris data or with data that is more than 2 hours old most GNSS receivers can get a new fix in a TTFF of less than 30 seconds in very good sky view conditions – known as a ‘cold start’. These TTF and TTFF times (typically advertised on the GNSS receiver data sheet) are best-case times. In reality it is unlikely for the GNSS receiver to start up in ideal sky view conditions when fitted to an animal. Any partial obstruction of the sky or adverse orientation of the antenna has an adverse effect on the TTFF and TTF. GNSS cellular tracking devices are configured to allow a finite amount of time for the GNSS receiver to successfully acquire a location. Depending on the device the time allowed to fix could be from 1 minute up to 5 minutes, after which it ‘times out’ and registers no position for that time. GNSS receivers that are fitted to animals that frequent dense vegetation, canyons or ravines can easily consume more than 4 times the power when compared those fitted to animals that roam open grass plains for example. Cloud cover and precipitation also attenuates signals from GNSS satellites – increasing TTF and therefore also the power consumption.
Cellular module power consumption
The other major contributor to power consumption is the Cellular module. Some Cellular tracking devices allow for a schedule to be configured so that multiple data points can be uploaded in one communication session. Saving multiple data points and sending them together saves some power as it takes time for the module to register to a network every time it sends data and therefore sending multiple data points in a session is more efficient. The trade-off for saving battery power through scheduled uploads is that the user will get less frequent updates of the latest location of the animal than if each location was sent at the time of its acquisition. Of course cellular network coverage is often poor where we are most interested in monitoring animals. Poor cellular coverage is bad for battery power consumption in three ways:
- higher transmit power is used because cellular modules adjust their transmit gain based on the strength of signal from the network,
- upload efficiency is reduced because failed data uploads need to be sent multiple times before they are successfully delivered and
- the time taken to register to a network and upload data is longer due to poor connections.
It is worth noting that cellular coverage is generally poorer when measured near the ground than it is higher up. Checking cellular network coverage whilst walking or travelling in a vehicle is often not representative of what the signal level will be on an animal in the same area. The height of the animal is generally lower than the level of a cellular phone held whilst walking or travelling in a vehicle.
Suitability of GNSS Cellular devices for different applications
Though larger than VHF transmitters, GNSS Cellular tracking devices can be quite small and can be used for tracking small or medium to very large animals. They are not suitable for very small animals such as rodents, birds 0r most reptiles.
For the purpose of comparison with the other technologies discussed in this guide we will consider the same applications again.
Physically finding an animal
When it is required to visually monitor an animal or a group of animals, the efficacy of GNSS Cellular devices depends on a few factors. If there is good cellular coverage in the area the animal frequents and the device is configured to regularly upload data, it is feasible for a field personnel to wait for the next upload and go searching in the area as soon as the location is uploaded. In poor coverage conditions however, it can be frustrating if the scheduled upload was unsuccessful. It is also difficult to get the location if the field personnel can not access the latest data due to poor cellular reception on their phone or laptop. If the tracking device is configured to upload data infrequently to save on battery life, it can be inconvenient to have to wait for a very long time for the next upload from the tracking device. For these reasons a VHF transmitter is often included in a GNSS cellular collar. The field personnel would use the last received location as a starting point to search for VHF signal from the transmitter as described in the chapter on VHF transmitters.
Collecting location data
Good GNSS Cellular tracking devices capture and store location data and automatically upload the data to a platform for the user to access. When compared to VHF transmitters where data collection is manual:
- The act of physically tracking the animal regularly is not required and the use of the technology does not alter its behaviour due to the field personnel’s proximity to the animal.
- Each location point is automatically captured and it is therefore easy to get a rich data set if the environmental conditions allow.
- The collection of location information does not consume a lot of costly resources – e.g. no field personnel, vehicles or fuel needed.
- As apposed to VHF transmitters, getting animal locations at night time from a GNSS Cellular tracking device is no more challenging than getting them in the day. This allows for safer studies on nocturnal animals.
- The efficacy of GNSS Cellular collars are dependent on terrain and cellular network coverage.
Collecting other data
If more information such as activity level or temperature is needed, a GNSS Cellular tracking device can easily include that in the data set with minimal impact on battery consumption or costs.
GNSS Cellular tracking collar costs
GNSS Cellular tracking collars cost more than VHF transmitter collars, and generally have an associated service fee for platform access and data costs. The additional costs are however quickly recovered due to the automation and low cost of use.
Cost of Equipment – Medium
The cost of a GNSS Cellular collar is higher than that of a pure VHF transmitter collar but the cost is mid-range when comparing to a collar containing any of the other technologies in this guide.
Cost of Deployment – High
Fitting and removing tracking collars to wildlife is very expensive. Depending on the animal being collared, various techniques are used to capture and often tranquillise the animal before fitting the collar. It is sometimes necessary to charter spotter airplanes, helicopters and specialised wildlife veterinarians to get the job done. The total cost in resources to locate, tranquillise and fit tracking devices to animals can sometimes exceed the costs of the tracking equipment.
Service Fees – Medium
There is typically a service fee associated with GNSS Cellular collars. The fees generally cover the cost of the provider’s platform and the cellular network charges. Fees may be charged on a monthly basis, or bundled into the upfront cost of the collar.
Cost of Use – Very Low
During normal operation there is no intervention required for a GNSS Cellular tracking collar to acquire and upload data for access by the user. These devices can collect a lot of data and provide rich data sets.
Total Cost – Medium to Low
When considering all costs, GNSS Cellular tracking collars are very cost effective at gathering data because this is done automatically without any manual field work required. When used in good cellular coverage and with the correct configuration for their environment they offer very good cost per location for very little user effort.GNSS Cellular Technology rating
Reliability – Very Good
When used in good coverage GNSS Cellular collars can be very reliable. Whilst they are quite small in size these days, there is more electronics and batteries that need to be housed in a collar or harness than is the case for a VHF transmitter. The bulkier a collar, the more chance it has of suffering damage due to bumps, bites or wear whilst deployed. More components also increase the chance of a critical component failure – although these are very rare and there is a greater chance of physical damage or shock on the housing to be a root cause of failure.
Ease of Use – Excellent
For data collection there is nothing for the user to do. The GNSS Cellular tracking collar and the provider’s platform perform all the heavy lifting and data is delivered to the user wherever they may be.
Data granularity – Very Good
Data granularity can be very high. The amount of data that can be collected depends on the duration of the deployment, the amount of batteries that are accommodated and the schedule of data collection and upload.
Battery Life – Good to Very Good
Battery life of a GNSS Cellular tracking device depends on the configured logging and upload schedule, animal behaviour, terrain and cellular coverage. On the whole, if configured correctly for the situation, these devices offer good battery life for medium to large animals that can carry a medium sized battery pack.
Things to consider when ordering a GNSS Cellular collar
Check whether the target animal is likely to spend a good proportion of time in cellular coverage as this will improve the regularity of data uploads. It is also important to ensure that your provider fits the tracking device with a SIM card for the network with the most coverage in the area.