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A new method makes it possible to map desert lakes around the world from space

Prof. Moshe Armon: "The method we developed can be used to map the bottom of desert lakes around the world, and help us understand what the climate was like in those regions of the world in the past and maybe even in the future"

Aerial photograph of Lake Eyre in Australia. Photograph from the study
Aerial photograph of Lake Eyre in Australia. Photograph from the study

Lakes in desert areas are usually shallow (several meters) and very flat, and mostly far from populated areas. Most of the time they are completely empty of water, but occasionally they are filled by rare floods that flow through the desert. This amount is obviously not sufficient to reach the place with a ship, and map the shape of the bottom of such lakes - so we cannot measure and determine in a reasonable way how much water the lakes store at any given moment.

אגם אייר באוסטרליה. צילום מתוך המחקר"Typically, a desert flood is lost into the stream bed and absorbed into its infrastructure or evaporates, therefore disappearing down desert rivers. Once in a few years such a flood may reach a shallow desert lake located downstream of the stream and fill it and gradually, the water that has stood in the lake evaporates from it. This is also how, for example, an oasis can be created," explains Koko (Moshe) Armon from the Institute of Earth Sciences at the Hebrew University. "Desert lakes may serve us as large natural water reservoirs, and they are home to a very large variety of species of desert plants and animals that only manage to thrive during floods. These lakes are used by climate researchers in order to understand what the climate was like in ancient times and try to extrapolate from that to the future. For example, if we identify a period when the lake was frequently full, we can understand that the climate was wetter. But 'more' is a relative concept and our goal is to determine how wet it was in those places."

In order to understand the amount of water in a desert lake, it is necessary to know what the exact topography of its bottom looks like - a job that is considered very difficult to perform in desert lakes. Koko (Moshe) Armon recently conducted a study in which he examined an original method for determining the topography of desert lakes. About a year ago he and his colleagues published a scientific article that appeared on the cover of the journal "Geophysical Research Letters". Now the article and the original method are being rediscovered by the American space agency NASA, which published an article about it today (Tuesday) at the NASA Earth Observatory. His research was carried out by Armon together with (in order in the article) Dr. Elad Dante (The Institute of Earth Sciences at the Hebrew University, the Geological Institute and the Shamir Institute), Yuval Shmilovich (The Institute of Earth Sciences at the Hebrew University and the Geological Institute), Dr. Amit Moshkin (Geological Institute), Prof. Tim Cohen (University of Wollongong in Australia), Prof. Efrat Morin and Prof. Yehuda Anzel (both from the Institute of Earth Sciences at the Hebrew University).

The research actually started about two years ago, when a new NASA satellite (ICESat-2) was launched whose original function was to measure very precisely the height of the glaciers in the poles - to better understand how global warming affects the loss and thinness of the ice in the poles. The exact height measurements were made possible by means of a laser projected from space to the surface of the earth. Thus, if you measure the time it takes for the laser beam to return from the surface of the earth to the satellite, you can accurately calculate the height of the surface. The satellite is unique in that it measures the height of the surface very precisely, with the help of a green laser beam. Since green light is able to penetrate several meters into water and still return to the satellite, accurate height measurements can be obtained through the satellite even underwater, at a very high density along narrow measurement corridors.

"Penetration of the light to a depth of a few meters is all we needed in the case of shallow lakes," explains Armon and adds that "using the results obtained from the new satellite, we were able to find, analyze and describe in our research the relationship between the frequency of the appearance of water in each area of ​​the lake (from a long series of photographs other NASA satellites, over the years), and between the height of those areas (from the new satellite). Once we know what the connection is, we can accurately calculate the depth of every point in the lake, even though the original depth measurement is only done along narrow corridors in it, and even if the lake is full of water."

The researchers used a method they developed to map the bottom of the largest shallow desert lake in the world - Lake Eyre in Australia, which is almost a third of the area of ​​the State of Israel, and obtained results that are almost certainly, according to the researchers, better than those measured in the lake itself using research ships in the 70s the former Following the results, the researchers decided to map two more desert lakes that until now had no way to understand the amount of water stored in them. One of them is called Sabhat al-Malh, which is in the Sahara Desert in Algeria and the other is called Lago Cuipsa and is in the dry Altiplano in Bolivia, on the itinerary of many of the Israeli backpackers in South America. Regarding Lago Kuipsa, for example, the researchers were able to discover that the amount of water that can be stored in the lake is 50% greater than what was commonly thought until now. Such an amount probably filled the lake about 12,000 years ago, but the water gradually disappeared and today the lake is only partially filled.

Armon concludes and states that "the method we developed can be used to map the bottom of desert lakes around the world, and help us understand what the climate was like in those regions of the world in the past and maybe even in the future. We are sure that we will be able to develop the method over time, this is just the beginning. In order to better prepare for climate change in desert areas we must know how much natural water exists in them, but until now it has been very difficult to do so. In the future, we will be able to estimate with a high degree of accuracy the amount of water in all the desert lakes around the world."

for the publication of the scientific article

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