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What is Satellite Tracking?

Three forms of radio tracking systems are used in today’s day and age: Very High Frequency (VHF) Radio, Satellite Tracking, and Global Positioning Systems (GPS). In this post I will discuss VHF radio tracking as a means of introducing and facilitating the comprehension of satellite tracking.

VHF radio tracking has been around for decades and involves placing a radio transmitter on a sedated animal, which then transmits information to a radio antenna and receiver. Locating animals using this technology means a researcher must be within close enough range to pick up the transmission coming from the animal. Due to the large size of older radio transmitters, they were previously only able to be used on large animals; However, technological improvements have allowed scientists to create smaller transmitters. In fact, some transmitters can even be ingested or placed under skin, meaning they can now be used on a wider variety of animals.

Satellite tracking is a lot like VHF radio tracking, but instead it uses a satellite instead of a radio transmitter. This simplifies the tracking process, because researchers are able to record all of the same information through a computer that is connected to a satellite .This means the researcher isn’t required to be anywhere near the animal(s) they are observing, which allows information to be recorded virtually 24 hours a day.

Tracking technologies have been around for decades, providing researchers with the ability to record information about occurrences that they do not need to be physically present for- or even near for that matter. Through the lens of conservation biology, this can include observing daily movements of animals, determining their home range, how these animals interact with other species in their geographic range, and the types of habitats these animals use. Understanding this information allows researchers to discern how they might control animal populations, determine potential effects from development on animal populations, and if the population of a given species group is large enough to allow for successful reproduction.

(**All above information was taken from: NH PBS’s Wildlife Journal Junior)

The above image is provided by Pettorelli et al. (2014) and is described as follows:

“Main sensor types on‐board satellites. Passive sensors measure natural radiation emitted or reflected by the Earth: reflected sunlight is the most common source of radiation measured by these sensors. Multispectral imagery is produced by sensors that measure reflected energy within several specific broad bands of the electromagnetic spectrum; hyperspectral sensors, on the other hand, measure energy in narrower and more numerous bands than multispectral sensors resulting in a relatively continuous measurement of a portion of the electromagnetic spectrum. Active sensors emit an electromagnetic pulse and later measure the energy bounced back to them: RAdio Detection And Ranging (radar) sensors on‐board satellites use longer wavelengths (microwaves) and are side looking (off‐nadir), while light detection and ranging (LiDAR) sensors emit laser pulses (usually at 1064 nm) and are nadir viewing.”

References:

- Pettorelli, N., Laurance, W. F., Obrien, T. G., Wegmann, M., Nagendra, H., & Turner, W. (2014). Satellite remote sensing for applied ecologists: Opportunities and challenges. Journal of Applied Ecology,51(4), 839-848. doi:10.1111/1365-2664.12261

- Wildlife Journal Junior. (n.d.). Tracking Wildlife. Retrieved from https://nhpbs.org/wild/tracking.asp

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Sea Turtles and Satellite Tracking

Image taken from Caribbean Journal

Satellite tracking technology is currently used by numerous researchers to study population levels, dispersal, life histories, behaviors, foraging habits, potential mortality risk, and best conservation practices of sea turtle species around the world (Jeffers & Godley, 2016; Maxwell et al., 2011; Scott et al., 2012; Schofield et al., 2013). Historically speaking, sea turtles have been rather difficult to study given their wide habitat ranges and elusive nature. However, with the help of satellite technologies, researchers have been able determine the movements of olive ridley sea turtles (Lepidochelys olivacea) in Central Africa over the course of two years. The results showed that most turtles remained within 30 km of their nesting zone during breeding seasons before setting out for distant foraging grounds (Maxwell et al., 2011). Scott et al. (2012) note the importance of tracking dispersal patterns and habitat use of the Mediterranean loggerhead turtle (Caretta caretta) in order to determine optimal conservation zones for turtles. This concept is important on a global scale, considering satellite technologies have shown that green turtles are aggregated significantly more in Marine Protected Areas (MPAs; Scott et al., 2012). Ultimately, satellite tracking of sea turtles has helped researchers gather data on much more topics in a shorter span of time than could have ever been possible using strictly group-based methods. Given its immense abilities, straightforward results, propensity to long-term usage, and repeatability, it seems pretty clear that tracking technology truly has the potential to save not only individual species, but entire ecosystems!

Image taken from Sea Turtle Inc

References:

- Jeffers, V. F., & Godley, B. J. (2016). Satellite tracking in sea turtles: How do we find our way to the conservation dividends? Biological Conservation,199, 172-184. doi:10.1016/j.biocon.2016.04.032

- Maxwell, S. M., Breed, G. A., Nickel, B. A., Makanga-Bahouna, J., Pemo-Makaya, E., Parnell, R. J., . . . Coyne, M. S. (2011). Using Satellite Tracking to Optimize Protection of Long-Lived Marine Species: Olive Ridley Sea Turtle Conservation in Central Africa. PLoS ONE,6(5). doi:10.1371/journal.pone.0019905

- Schofield, G., Dimadi, A., Fossette, S., Katselidis, K. A., Koutsoubas, D., Lilley, M. K., . . . Hays, G. C. (2013). Satellite tracking large numbers of individuals to infer population level dispersal and core areas for the protection of an endangered species. Diversity and Distributions,19(7), 834-844. doi:10.1111/ddi.12077

- Scott, R., Hodgson, D. J., Witt, M. J., Coyne, M. S., Adnyana, W., Blumenthal, J. M., . . . Godley, B. J. (2012). Global analysis of satellite tracking data shows that adult green turtles are significantly aggregated in Marine Protected Areas. Global Ecology and Biogeography,21(11), 1053-1061. doi:10.1111/j.1466-8238.2011.00757.x

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Con: satellite tracking technology can be incredibly expensive.

While some satellite products are freely available, a significant amount are not, which has hindered the expansion of satellite monitoring in applied ecology and management (Leidner et al., 2012; Strand et al., 2007; Turner et al., 2013). Additional satellite technology can be pricey given the need for hardware, software, training, qualified staff, and any other logistical requirements needed to process and analyze large data sets (Pettorelli et al., 2014). Fortunately, open-source software and solutions are constantly on the rise, so hopefully this lack of access, documentation, and training opportunities will be addressed sooner rather than later!

References: 

- Leidner, A.K., Turner, W., Pettorelli, N., Leimgruber, P. & Wegmann, M. (2012) Satellite remote sensing for biodiversity research and conservation applications: a Committee on Earth Observation Satellites (CEOS) workshop. 

- Pettorelli, N., Laurance, W. F., Obrien, T. G., Wegmann, M., Nagendra, H., & Turner, W. (2014). Satellite remote sensing for applied ecologists: Opportunities and challenges. Journal of Applied Ecology,51(4), 839-848. doi:10.1111/1365-2664.12261

- Strand, H., Höft, R., Strittholt, J., Miles, L., Horning, N., Fosnight, E. & Turner, W. (2007) Sourcebook on Remote Sensing and Biodiversity Indicators. Secretariat of the Convention on Biological Diversity, Montreal, Technical Series no. 32, 203 pages.

- Turner, W., Buchanan, G., Rondinini, C., Dwyer, J., Herold, M., Koh, L.P. et al. (2013) Satellites: make data freely accessible. Nature, 498, 37.

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Pro: satellite tracking technologies offers long-term, repeatable, standardized, and verifiable information on key biodiversity indicators, which may otherwise be inaccessible.

Satellite remote sensing (SRS) is widely used by researchers due to its reliability and efficiency. Satellite sensing technologies offer information that would be inaccessible using only ground-based methods. SRS can be especially useful in understanding biodiversity, its pressures, and management consequences when combined with multiple SRS systems and/or ground-based methods as well. 

References:

- Pettorelli, N., Laurance, W. F., Obrien, T. G., Wegmann, M., Nagendra, H., & Turner, W. (2014). Satellite remote sensing for applied ecologists: Opportunities and challenges. Journal of Applied Ecology, 51 (4), 839-848. doi:10.1111/1365-2664.12261

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Con: satellite tracking may be an incredibly useful form of technology, however it is not available to everyone around the globe due to a lack of access to sufficient tools.

Researchers in biodiverse areas around the world could obviously benefit from the use of satellite data. Unfortunately, many of these places lack access to imagery or the appropriate tools for processing it. These limitations are often a result of sensor blockage, lack of finances, and/or security issues (Pettorelli, 2014). Some of these issues are even more prevalent in the more biodiverse areas. For example, large canopies block imagery, making visual transmissions near impossible.

References:

- Pettorelli, N., Laurance, W. F., Obrien, T. G., Wegmann, M., Nagendra, H., & Turner, W. (2014). Satellite remote sensing for applied ecologists: Opportunities and challenges. Journal of Applied Ecology, 51 (4), 839-848. doi:10.1111/1365-2664.12261

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Pro: satellite remote sensing (SRS) allows for a deeper understanding of species and ecosystems.

Sensor technology has come a long way since its inception. Even still advancements in methodologies and technology are being created year after year. At times, researchers combine different satellite sensors to come to more cohesive conclusions about a given species or ecosystem; Some case studies that focus on ecological issues using various forms of satellite remote sensing (SRS) are compiled in the table below (Pettorelli et al., 2014).

References: 

- Pettorelli, N., Laurance, W. F., Obrien, T. G., Wegmann, M., Nagendra, H., & Turner, W. (2014). Satellite remote sensing for applied ecologists: Opportunities and challenges. Journal of Applied Ecology,51(4), 839-848. doi:10.1111/1365-2664.12261