Why counting animals from spaces isn’t as hard as you think

Great Migration in Maasai Mara National Park, Kenya

Great Migration in Maasai Mara National Park, Kenya; copyright alextara / 123RF Stock Photo

Last week the keepers at London Zoo were busy counting their 17,000 animals, as part of the annual headcount. Knowing numbers is vital within the wild too, but counting animals on the plains of Africa is more challenging. Traditionally wild counts are either ground surveys, which take people and time; or aerial surveys, that can spook the animals. Satellite remote sensing could offer a potential solution, but it’s not straight-forward. Three papers published in 2014 show the possibilities, and challenges, of using satellites to count animals.

The paper Spotting East African Mammals in Open Savannah from Space by Zheng Yang et al (2014) published on the 31st December, describes the use of very high-resolution GeoEye-1 satellite images to detecting large animals in the Maasai Mara National Reserve, Kenya. GeoEye-1’s 2m multispectral image resolution was not sufficient to detect large animals. However, when combined with the panchromatic image using a pan sharpening technique the resolution improved to 0.5m meaning adult wildebeests and zebras were 3 to 4 pixels long, and 1 to 2 pixels wide. Experienced Kenyan wildlife researchers initially visually reviewed images to develop a classification system, forming the basis of a hybrid image system, using both pixel-based and object-based image assessment approaches to determine which pixels belonged to animals. The results showed an average count error of 8.2% compared to manual counts, with an omission error rate of 6.6%, which demonstrates that satellites have potential for use in counting; it’s cheaper and less intrusive than existing methods.

The second paper was published by Seth Stapleton et al (2014) entitled Assessing Satellite Imagery as a Tool to Track Arctic Wildlife. It used 0.5m resolution imagery of Rowley Island in Foxe Basin, Canada, from Worldview-2 to monitor the island’s polar bear population. The images were corrected for terrain and solar irradiance, and an a histogram stretch to brighten darker, non-ice, areas to assist human analysts identify the bears. Two observers visually identified ‘presumed bears’ both individually and jointly; resulting in the identification of 92 presumed bears. This satellite derived figure was consistent with other models, again offering a potential cheaper and safer way of monitoring polar bears.

Finally, Peter Fretwell et al (2014) published Counting Southern Right Whales by Satellite. Also using WorldView-2, they used a 2m resolution image with eight colour bands and one panchromatic band. The images were analysed using ENVI5 and ArcGIS to identify potential and probable whales, and then visual inspection of these images showed they had identified objects of the right shape and size to be whales; resulting in the identification of 55 probable whales and 23 possible whales. Again, showing satellite images could be useful in calculating whale populations faster and more efficiently.

All three of these papers demonstrate that satellite remote sensing has potential to assist in the monitoring of animal species across the globe. However, there are also significant challenges still to overcome, for example:

  • Resolution: Currently available resolutions may not sufficient to distinguish the level of detail conservationists need, such as species identification in Africa or polar bear cubs in the Canada. However, it may be possible with very high resolution satellites such as the planned WordlView-4 from DigitalGlobe.
  • Cloud cover: The persistent nemesis of optical Earth observation imagery may hamper it’s use in certain areas or seasons.
  • Complicated environments: Further research is needed to ensure animals can be accurately distinguished from their surroundings.

Despite these reservations, the potential to offer regularly, more efficient and safer methods of survey animal populations from space means this will be a rapidly developing area of Earth observation.

A Few Days In Portland: Phytoplankton, Sea Ice and Cake!

Early morning photograph of Portland, Maine

Early morning photograph of Portland, Maine

As I talked about in my last blog, this week I’m attending the Ocean Optics XXII Conference in Portland, Maine in the USA. I arrived last Thursday and spent the weekend at a two day pre-conference meeting entitled ‘Phytoplankton Composition From Space’; where we discussed techniques for mapping phytoplankton – the microscopic plants in the ocean.

The smallest phytoplankton taxa (group) are the single celled cyanobacteria known as blue-green algae, they are an ancient life form with a fossil remains of over 3.5 billion years old. They can be mapped from space using ocean colour satellites which measure a signal based on the scattering and absorption of light within the ocean. This enables Earth observation to map the total biomass, via the concentration of the main pigment that’s normally Chlorophyll, and also get a glimpse into which taxa are present.

Understanding the concentration, and diversity, of phytoplankton is valuable as they play a key role in climate processes by absorbing the greenhouse gas carbon dioxide. In addition, they are the very essence of the bottom of the food chain, as they are eaten by zooplankton, who in turn are eaten by small fish and so on. Therefore, significant changes in the concentration or diversity of phytoplankton may have ripple effects through the aquatic food chain. The film Ocean Drifters provides an overview of the role of plankton in the ocean.

The conference itself began on Monday and we’ve had a number of interesting and varied presentations, but I’ve particularly enjoyed two plenary sessions. The first was by Don Perovich, of the Thayer School of Engineering looking at the impact of sunlight on sea ice in the artic. The brightness of sea ice determines the amount of light reflected back to space. If the ice is older, and hence snow covered, then it’s bright white whilst ice that’s melting is much darker due to the pools of water and so absorbs more sunlight. Therefore, there is a positive link between melting ice causing ice to melt quicker. In the Artic, sea ice reaches a minimum in September and causes an increase in melting. There is a scientific analysis on Arctic sea ice conditions here.

The second plenary was given by Johnathan Hair from NASA Langley Research Centre, presenting a paper co-authored with his colleague Yongziang Hu and Michael Behrenfeld from Oregon State University. It focussed on using lasers for mapping vertical profiles throughout the water column from space and applications for inland waters, and how this might be used in global ocean plankton research. Regular readers of the blog will know this is topic is something that particularly interests me, and I have previously written about the subject.

Tuesday morning was eventful, as the conference venue was evacuated just as the first session was starting, due to a strong smell of gas. I took the unexpected networking opportunity, and to catch up with one of my former colleagues over a coffee. Thankfully, we were let back into the venue a couple of hours later, and everything went ahead with a bit of rescheduling. My plenary session on Crowdfunding Ocean Optics went ahead in the afternoon, and seemed to generate a good level of interest. I had lot of questions within the session, and a number of people sought me out during the rest of the day to discuss the idea and the project.

I’ve really enjoyed my time in Portland, and have found a fantastic coffee shop and bakery – Bam Bam Bakery on Commercial Street – which I highly recommend! I’m looking forward to the rest of the week.