In the Sahara and the Sahel, groundwater is a limited and indispensable resource for pastoral livestock farming. The daily life and work of the herders are organised around the location of the wells and the depth of the water table. To ensure the sustainable development of these regions, it is therefore essential to develop accurate piezometric maps, even in the areas that are most difficult to access. Thanks to high-resolution satellite images, the tracks made by cattle, goats and camels in the Sahara and Sahel could become a key indicator of the depth of the water table. In the northern Sahel, pastoralists water their livestock from deep wells. To draw water, they hitch oxen or camels to a rope whose length is an accurate measure of the depth of the piezometric surface of the water table. When pulling on this rope, the animals leave deep tracks on the ground that can be observed and measured on satellite images. We have developed a remote sensing technique that allows us to (a) identify pastoral wells, (b) isolate the tracks left by the animals used to draw water, and (c) use these animal tracks to estimate the water depth. After carefully calibrating the method, we were able to use open data (Landsat) and satellites images freely accessible data thanks to Google Earth Pro (SPOT and Worldview) to draw up, in just a few weeks, the piezometric map of a large aquifer (200,000km 2 ) that is not easily accessible by other means due to the prevailing insecurity that has persisted in this part of the Sahel region for several years. This same method was then subsequently tested and validated on two other aquifers, one in Nigeria and one in Niger.

中文翻译：

---

地下水位遥感的新工具：牧区水井的卫星图像

在撒哈拉和萨赫勒地区，地下水是牧区畜牧业必不可少的有限资源。牧民的日常生活和工作围绕着井的位置和地下水位的深度来组织。因此，为了确保这些地区的可持续发展，即使在最难以进入的地区，也必须绘制准确的测压图。多亏了高分辨率卫星图像，撒哈拉和萨赫勒地区的牛、山羊和骆驼留下的足迹可以成为地下水位深度的关键指标。在萨赫勒北部，牧民从深井中给牲畜浇水。为了取水，他们将牛或骆驼拴在一根绳子上，绳子的长度可以精确测量地下水位测压表面的深度。当拉上这根绳子时，这些动物在地面上留下很深的痕迹，可以通过卫星图像进行观察和测量。我们开发了一种遥感技术，使我们能够 (a) 识别田园水井，(b) 隔离用于取水的动物留下的痕迹，以及 (c) 使用这些动物痕迹来估计水深。在仔细校准该方法后，我们能够使用开放数据 (Landsat) 和卫星图像免费访问的数据，这要归功于 Google Earth Pro（SPOT 和 Worldview），在短短几周内绘制了大型含水层的测压图（ 200,000 公里 2 ) 由于萨赫勒地区这一地区多年来普遍存在的不安全状况，无法通过其他方式轻易到达。随后，同样的方法在另外两个含水层上进行了测试和验证，一个在尼日利亚，一个在尼日尔。