GPS Wildlife Tracking – Terminology

When you understand GPS wildlife telemetry basics you put yourself into a powerful position with increased probability that your GPS telemetry work will succeed. Here are a few fundamentals to help get started.

Stored activity data that relates to animal head movement up and down and from left to right (indicating walking).

A two-dimensional GPS position fix that includes only horizontal coordinates (no GPS elevation) requiring at least three visible GPS satellites.

A three-dimensional GPS position fix that includes horizontal coordinates, plus elevation requiring a minimum of four visible GPS satellites.

We strongly suggest that you get familiar with your GPS equipment prior to deployment. Part of this process is to determine general position accuracy in your field conditions. After deployment, unless you observe the study animal at the precise time of a GPS location attempt, there will be no way for you to determine position accuracy. People talk about the quality of the position’ indicated by PDOP. Don’t bet your life on that, put the effort in and go out in the field to see what the accuracy really is. And don’t be misled or confused by telemetry manufacturers claims of any particular accuracy for most positions. Without position correction this claim is impossible to verify. However, it may be that a GPS chip manufacturer claims something like 5 meter accuracy 95% of the time. And that may be well and true in a GPS chip manufacturers tests . . . which are highly controlled and have nothing to do with the performance of a GPS collar built with that GPS chip!

There is a direct relationship between overall battery life and GPS position accuracy and with Telemetry Solutions products you are in control over this relationship. If you are more interested in long term battery life and less interested in accuracy, so be it . . . just set the GPS unit up for that, it’s simple. On the other hand, if you want very accurate data (which you will verify by testing before deployment) we have a way for you to set the product up for that. It’s really simple to do this. Of course there is always a middle ground for those interested in compromise.

This is the product feature that allows you to set up the GPS unit to perform as you wish in regard to accuracy versus battery life. For maximum battery life set to 5. For maximum accuracy set to 40.

Information stored in the GPS collar memory and/or transmitted over the VHF beacon that indicates the level and the type of movement by the study animal.

Information, transmitted by each satellite, on the orbits and state (health) of every satellite in the GPS constellation. Almanac data allows the GPS receiver to rapidly acquire satellites shortly after it is turned on.

Collars seem to be the most popular method for attaching GPS data loggers to most mammals. Ear tags can be used for certain species. Backpacks work for many birds as do tail mounts and necklaces. We even made a GPS snake implant which contradicts some of what we said in the section above entitled GPS Signal Strength. Glue on is another method for birds and also tortoise and turtles. We have customers using a waist band attachment on small frogs. Our GPS pods are quite popular for those working with large mammals on a strict budget. Use your imagination and make the request . . . users often devise new and unusual ways of doing these things. Here is more information on some of the most popular attachment types.

With the exception of cattle and certain bear applications we build all of our collars from scratch using the raw material of choice for the application. Some material examples include chrome suede, nylon, stainless steel cable in a PVC tube, neoprene, cable ties and a plastic coated polyester material. If you see a collar representation on this website that isn’t exactly what you would like, just ask us if there is another choice, there probably is.

Collars are generally built at a mean neck circumference with some amount of user adjustment around the mean. Because there is generally a GPS antenna on the top of the collar we like to have a mean circumference determined by you so that we can build the collar such that the antenna is right at the top of the neck when adjusted to this mean size. Theoretically a GPS antenna positioned in this way will result in better performance than antennas down one side of the collar. But in reality we have seen field results from GPS antennas intentionally placed at the 9 o’clock position (on African lions) that are the same as antennas placed at the 12 o’clock position on the collar.

Specifying a collar width is also within the purview of the user. We don’t tell you how wide the collar will be, you tell us. If you don’t know then we can make suggestions.

By not using housings we reduce not only the product weight but also the bulk of the package. Collar housings look nice but they add unwanted weight and bulk. Most of the products that Telemetry Solutions makes lend themselves quite nicely to conformal coating rather than putting the electronics and batteries inside housings. We have ways to make even really heavy battery configurations stay attached to collars without housings. These methods are not new, we have been using them for many years and they work.

Telemetry Solutions’ GPS backpacks are offered over a significant size and shape range. The topics above explain why. After leaning the species to be equipped we then determine the battery choice followed by the GPS antenna choice which can greatly influence the size and shape of the GPS backpack. In the case that there is a VHF transmitter in the package considerations such as antenna angle come into play. As usual we encourage your input in this design process but if you haven’t got experience with the species in question we will advise you. Our backpacks normally include some forms of passageways for your harness but we don’t include the harness as they vary greatly from user to user.

The GPS pod concept is simple. We manufacture the GPS component and enclose it in a housing with the batteries. No wires exit the pod, it is just that, a pod. We provide attachment hardware for you to use to add this to the top of a VHF collar of your choosing. Voila, a GPS collar. As usual you have a choice of battery size and options such as remote data download (UHF or satellite or both) and solar power is also an option.

An alternative power source in the GPS collar that provides current to the drop off mechanism and the VHF recovery beacon even after the primary power source has gone flat.

Some of the factors that influence the battery life of your wildlife tracking device are temperature during the study, the type of battery used, the length of time the GPS turns on to acquire a GPS position, how much of that time is spent calculating a GPS position and how much is spent trying to acquire satellites (these are very different), the type of GPS antenna used and whether or not the device is also sensing activity information! If that’s not enough there is another very, very important factor that influences the battery life of a tracking device and that is the battery itself. At Telemetry Solutions we have spent thousands of dollars testing batteries on our devices right here in the shop. These batteries never end up in a customer’s product but are chosen at random from our battery stock. In controlled testing conditions where we can measure the current draw of every part of the process we have found that new batteries last anywhere from 80% – 120% of the time they should last. We have repeated this test over and over and have come to the same conclusion each time. In addition, we have performed this test with equivalent batteries from different manufacturers and again we have had the exact same results. As the end user you must take this into consideration when planning your project.

We mentioned this feature in the section above about GPS signal strength but it is getting mentioned again because it has a major impact on battery life too. For units that are in the lower weight range of our product line this feature can have substantial impact on battery life.

A user created timetable that indicates to the GPS collar when to attempt GPS position fixes and when to transmit a VHF signal, among other things.

The distance from which a user can successfully retrieve GPS position data that is stored in the GPS collar memory and transmitted to the user on command.

A mathematical model that depicts a part of the surface of the earth. Latitude and longitude lines on a paper map are referenced to a specific map datum. The map datum selected on a GPS receiver needs to match the datum listed on the corresponding paper map in order for position readings to match.

An extension of the GPS system that uses land-based radio beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of selective availability, propagation delay, etc. and can improve position accuracy to better than 10 meters.

A measure of the GPS receiver/satellite geometry. A low DOP value indicates better relative geometry and higher corresponding accuracy. The DOP indicators are GDOP (geometric DOP), PDOP (position DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time clock offset).

A device built into the GPS collar that will allow the user to remotely cause the GPS collar to fall off of the study animal on command.

Depending upon the application we use different methods of encapsulation. We have about 10 different types of encapsulation available depending upon the application. The most common is a conformal epoxy coating applied by hand. This is generally the best compromise for small animal GPS collars that need to be waterproof, durable and lightweight. We always use the encapsulation that makes the best product, don’t be afraid to ask about this during the ordering process.

Some of our products have the epoxy conformal coating, some are encased in plastic/fiberglass housings, some are coated in a combination of plastics while others are encapsulated using molds and various types of encapsulant. It all boils down to your application.

Usually for bird applications we keep the coating to a minimum, each coat adds at least .3 grams. Working with total product weight limits less than 10 grams may result in minimal encapsulation but if the application warrants anything other than minimal encapsulation we will certainly take that into account and encapsulate appropriately.

For small GPS collars this normal encapsulation will add anywhere from 10-15 grams. Please don’t be confused by this, on our websites all weights are specified as final weights. The encapsulation must be applied to all batteries and electronics including the GPS antenna at the top of the collar. This normal encapsulation will prevent water damage to the product but may not provide the optimum protection from damage during predation. In other words, a predator can destroy or at least damage these devices if they set their mind to it.

If you know that your study animals are going to partake in behavior that is particularly destructive to the tracking device please tell us this in the ordering process. We have a short questionnaire in our order form that provides the vehicle for you to convey this information. At this point we may suggest a stout type of encapsulation that will probably consist of a hard outer shell with the batteries and electronics residing in something akin to a mother’s womb.

The Global Orbiting Navigational Satellite System; the Russian counterpart to the United States’ GPS system.

A global navigation system based on 24 or more satellites orbiting the earth at an altitude of 12,000 statue miles and providing very precise, worldwide positioning and navigation information 24 hours a day, in any weather. Also called the NAVSTAR system.

The time it takes a GPS receiver to acquire satellite signals and determine the initial position.

Because signals from GPS satellites are wireless, the GPS receiver must capture these signals with an antenna. Whether the tracking device is a collar, backpack or any other type of attachment, the antenna is built into the tracking device. There are many things that affect the GPS antenna’s ability to receive that signal and without a signal from at least 3 satellites the receiver won’t be able to calculate a position. Maximizing the received signal strength is key. Here is a bit more information about the GPS signal, what affects it and what we can do to mitigate these is sues.

GPS signals won’t penetrate water. Stand outside with a handheld GPS device, turn it on and leave it on. Let it acquire satellites then put your hat over the GPS antenna. Nothing will happen, the unit will just keep working. Now put your hat back on and put your hand over the GPS antenna. The water content in your hand will block the GPS signal and the receiver will lose those satellites. So we can’t expect a GPS receiver implanted in an animal to acquire satellites and we can’t expect a GPS unit on an aquatic animal to acquire satellites . . . at least not while the antenna is under water. To some extent the same goes for snow if it is deep enough to cause a problem. This could be snow over a den the animal is in or it could be snow in the forest canopy.

Another issue with signal strength comes into play when a small animal wearing a GPS collar curls up for a sleep. Laying on their side the GPS antenna loses most of the sky view it needs for a GPS position. Compound that with a resting place that is already well blocked off from GPS signals and the result is reduced GPS positioning success. But Telemetry Solutions has devised a solution for this and it works great. It’s called Smart GPS.

There are many types of GPS antennas available in our telemetry products and not all antennas perform the same. Generally the bigger the better but in our applications bigger isn’t always possible. When possible we will include an antenna enhancement for your equipment and we will always use the best antenna possible within the confines of your application.

A position’s distance north or south of the equator, measured by degrees from 0 to 90. One minute of latitude equals one nautical mile.

The distance east or west of the prime meridian (measured in degrees). The prime meridian runs from the north to South Pole through Greenwich, England.

This device enables a user with a magnet to turn off a GPS collar after programming but prior to deployment.

The most locations that a GPS collar can acquire before its primary battery is depleted.

The instances of no location data acquired by a GPS collar when a GPS position was attempted.

GPS position data that is stored in the GPS collar memory and transmitted to the user over the GSM mobile phone network.

A memory chip that does not require a power source in order to retain information.

Extending the battery life and increasing the number of successful GPS positioning attempts in very small GPS backpacks and collars, Smart GPS is a powerful tool. The user interface allows you to customize the performance characteristics of this option but expect a significant time commitment to be successful.

Some people consider the activity data more important than the GPS data. Our activity option is capable of capturing fine scale movements, isolating particular movements, filtering out unwanted activity information and outputting the total intensity of all movements within a specified sampling time. It also includes a user interface that allows you to actually view data in real time at your computer while you hold the GPS device and move it in various ways to represent the activity of an animal.

Telemetry Solutions offers two different technologies when it comes to remote data transfer. One requires the user to be in the field, the other does not. They both have pros and cons, please see the next two sections to learn more.

The beauty of the UHF system to transmit GPS data remotely is that we can make it very, very small and it consumes almost no power to transmit the data. The system is therefore on demand and the user will need to be in the field within range of the signal. The signal offers maximum data transfer range of 400 meters line of sight. This does not mean, however, that every attempt at a remote download has a 400 meter range, there are many factors that affect the download range. Two things that you can do to maximize download range are to gain altitude over the study animal and to use the appropriate antenna that we will sell to you.

In this day and age many of us expect information at our fingertips. For a very long time there have been systems that transmit GPS data from animals in the field to your computer screen. These systems are somewhat antiquated and will shortly be surpassed by new technology, the writing is on the wall for even the smallest satellite transmitters available. Telemetry Solutions offers a product with satellite data transmission to a password protected website via a much more modern satellite communication system. The beauty of the system is that the data transfer fees make it very affordable. The drawback of this system is that it’s still a bit big and only appropriate for animals that can carry several hundred grams. As usual our system allows the user to determine how often data are sent as well as exactly when GPS positions are attempted by the product.

Information supplied to the user by the GPS collar whether supplied by mobile phone download, radio download or direct download via a custom USB cable.

GPS position data that is stored in the GPS collar memory and transmitted to the user via a 433 MHz transceiver.

With our products, scheduling GPS positioning times is not only simple but very flexible as well. For our non-solar products these are different ways that you can schedule GPS positioning.

Repeat mode means that you will set the interval between positioning attempts. The minimum is 2 minutes the maximum is 48 hours 59 minutes. You can pick an interval anywhere between the minimum and maximum and set the GPS receiver to turn on every time that interval elapses.

You can easily use template mode to schedule GPS positions. This is a very powerful feature whereby you indicate specific times in the day for GPS positioning. When you have assigned the scheduled GPS positioning times for a particular day you have created a template. After that you may continue to create up to 19 more unique templates so that you can have GPS positioning at different times on different days. You can also create a template with no GPS positions scheduled. After you have created all of these templates then you apply the templates into the days in the year. Mix them up as you see fit. If there are times when you don’t want any GPS positions then just use that template that you created with no location attempts in the day! It could not be simpler. Program the current year and the next and the next, each year’s schedule can be different.

If it is interesting to you to get a short burst of extremely frequent positions use the always on mode and schedule GPS positions every 5, 10 or 20 seconds. A word to the wise, this eats battery power.

This is a special product that only operates in this one mode. In this mode, every time enough energy is accumulated a GPS position is taken. On very sunny days you may have as many as 60 positions per hour. The catch is that it won’t work in the dark . . . we have solar units that will but not the one that uses the energy immediately.

You have the ability to set a time period considered to be daytime. Within this period your GPS wildlife device will follow one of two possible daytime GPS positioning intervals. You set both intervals and depending upon available battery voltage the device will follow one or the other. Remember that the interval is the time between GPS positioning attempts. The two different daytime intervals that you can set are called full and middle

  • Full BatteryIf battery voltage is from 3.6 – 4.1 volts the battery is considered to be full and the GPS device will follow the more aggressive of your two daytime schedules. In other words, since there is more battery voltage available you can schedule more GPS positioning attempts. You will set the number of minutes between positioning attempts.
  • Middle VoltageWhen the voltage is dropping due to the lack of sunshine on the solar panel, when the voltage drops down below 3.6 volts a less aggressive interval will be followed. We call this middle voltage. It is comparable to slowing down your car to save gas when the tank falls below 1/4 full. If the battery goes down as far as 3.35 volts the device goes to sleep. When enough power is generated by the solar panel and the battery is charged back up to 3.6 volts the unit will wake up from sleep mode and begin to operate again in middle voltage mode.

If you want to, you set a time period to be defined as nighttime. During this period you can have the device follow two different positioning intervals. The reason that we offer the ability to define day and night and to change the GPS positioning intervals is so that you can decide to devote battery voltage to positions taken either at night or in the day . . . regardless of the interval. If you are not interested in positions in either day or nighttime then its easy enough to just set the interval very long during this time, thereby saving battery for the part of the day when you want the most positions.

  • Full BatteryThis is the same as described in the full mode above. If battery voltage is from 3.6 – 4.1 volts the battery is considered to be full and the GPS device will follow the more aggressive of your two daytime schedules. In other words, since there is more battery voltage available you can schedule more GPS positioning attempts. You will set the number of minutes between positioning attempts.
  • Middle VoltageWhen the voltage is dropping due to the lack of sunshine on the solar panel, when the voltage drops down below 3.6 volts a less aggressive interval will be followed. We call this middle voltage. It is comparable to slowing down your car to save gas when the tank falls below 1/4 full. If the battery goes down as far as 3.35 volts the device goes to sleep. When enough power is generated by the solar panel and the battery is charged back up to 3.6 volts the unit will wake up from sleep mode and begin to operate again in middle voltage mode.

Just like the template scheduling mode described above this works by following different daily GPS positioning schedules that you create. However, with the solar products there is always the chance that the device will go into sleep mode when the battery voltage drops low due to lack of sunlight on the solar panel.

A GPS collar that acquires GPS positions and stores them but does not transmit them to the user remotely. A user must recover this collar to extract the data manually via a wireless or a USB connection between the collar and the user’s PC.

The lowest and highest temperatures at which a GPS collar will still continue to operate properly. The collars are not guaranteed to operate properly outside of this temperature range.

The time needed to acquire a GPS position is the primary factor affecting battery life. More than habitat type or topography the time needed to acqurie a GPS position is determined by whether the location attempt is the result of a hot start, warm start or cold start. The GPS hardware in wildlife tracking devices is a receiver only. Regardless of whether or not the device has a data transmitter on board the GPS part is only a receiver. It receives signals and from the information in that signal calculates its position. There are three ways that a GPS can start this process.

When the GPS has in its memory information about its last calculated position such as; which satellites were used to calculate the position, which almanac was used and the UTC time, a new position can be calculated in less than 1 second. This is called a hot start. In addition to meeting the requirements above, it only works when the GPS is in the same general location as the last time it acquired a position and if not too much time has elapsed since that last location was calculated. This is a real battery life saver but contrary to popular belief a hot start is not always precise.

If all of the criteria for a hot start are met, with the exception of which satellites were in view for the previous location calculation, the result is a warm start. It takes longer than a hot start and can range up to about 25 seconds. Obviously this uses more battery life.

When none of this information is available, the GPS receiver has lost it all, the result is a cold start which will require about 35 seconds or more in order to calculate a GPS position. Even more battery is used.

The conclusion is that, depending upon your needs, you can sometimes extend battery life by scheduling more frequent GPS positions. This is counter intuitive and requires some trial and error in your particular habitat.

Universal Transverse Mercator. A nearly worldwide coordinate projection system using north and east distance measurements from reference point(s). UTM is the primary coordinate system used on U.S. Geological Survey topographic maps.

The most important constraint in most wildlife telemetry transactions is the weight of the product that the customer will purchase and use. Needless to say Telemetry Solutions specializes in micro GPS telemetry devices and we can make them as light at 2 grams total weight. But this isn’t a very practical solution and most researchers can afford much more than 2 grams. Various product attributes affect total product weight but not every feature adds weight. Let’s focus on those that constitute weight.

Almost always the heaviest part of a wildlife GPS tracking device is the batteries. On the big side, a D cell used in these applications weighs 90 grams. Imagine trying to make a GPS collar with a weight restriction of 200 grams and having to use a D cell battery to meet the customer’s battery life specifications! On the other end are 1/2 AA batteries that only weigh 9 grams. Ahhh, much easier. But wait . . . they aren’t easier because the product weight restriction just shot down to 30 grams! It’s more difficult to build lightweight tracking devices than it is to build heavy ones.

Telemetry Solutions uses two types of batteries, lithium thionyl chloride batteries and lithium polymer batteries. The former is a primary battery, the latter is rechargeable.

We almost always use a separate battery system to power the GPS portion of our products. The VHF side has its own power supply. Telemetry Solutions can choose from about 7 or 8 different sizes of primary batteries or up to 50 different rechargeable batteries to make your GPS tracking units. And we sometimes use multiple batteries in one application. The reason for the wide variety is that they represent a broad range of sizes and weights. Our goal is to configure your product in such a way as to strike a balance between product weight and performance. But don’t worry, you won’t be expected to know anything about batteries; we’ll choose the right battery based on conversations with you during the sales process.

As with the GPS battery, we have a wide range of choices when it comes to the VHF battery. You are not expected to know which battery to use. How we place the GPS and VHF batteries in the package is very important in terms of the shape of the electronics package. Again, this is a user’s choice. Please contact our sales representative who will help you determine what you need for your project.

World Geodetic System, 1984. The primary map datum used by GPS. Secondary datums are computed as differences from the WGS 84 standard.

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