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OBSERVER: Monitoring soil moisture from space with Copernicus | |
admin | |
2020-02-20 | |
发布年 | 2020 |
语种 | 英语 |
国家 | 欧洲 |
领域 | 气候变化 |
正文(英文) | OBSERVER: Monitoring soil moisture from space with CopernicusIn this edition of the Copernicus Observer, we will look at the ways soil moisture is being monitored through the Copernicus programme. In a previous Observer edition, we talked about how the Copernicus services were involved in monitoring and tracking the unprecedented Australian bushfires. One of the key factors that influenced this catastrophe was severe drought. The fires fed off high temperatures and low soil moisture. Monitoring soil moisture is becoming a very important tool for predicting and monitoring possible disasters. Nowadays, synergies between different satellite systems enable us to monitor soil moisture at an unprecedented regularity and scale. In this aspect, Copernicus plays a crucial role. Soil moisture is a key variable regulating the exchange of water, energy, and carbon cycles between the land and the atmosphere. Soil moisture data is therefore essential for various environmental studies, including hydrology, climatology, meteorology, agriculture, water resource management and climate change. This is why soil moisture is recognised as one of the Essential Climate Variables defined by the Global Climate Observing System, which assesses the status of global climate observations and produces guidance for its improvement. A number of in-situ techniques have been developed over the past decades to measure soil moisture. However, they are restricted to specific area measurements, and do not represent soil moisture distribution over larger areas, as soil moisture is highly variable in both space and time. Fortunately, current technological advances in satellite remote sensing have offered an alternative to field measurements and have enabled us to monitor it at higher temporal and spatial resolutions, and at a considerably lower cost and time. The Copernicus programme is a frontrunner in this field. Copernicus Global Land service, Daily Surface Soil Moisture based on Sentinel 1 over Europe, 24 Aug 2018 Three ways to measure soil moistureThere are three types of sensors that can be used for soil moisture estimations. Multispectral sensors (such as Sentinel-2) take advantage of the information available from visible, near-infrared, shortwave infrared, and thermal infrared portions of the electromagnetic spectrum. Most techniques have developed an empirical spectral vegetation index, which indicates certain vegetation characteristics, thus allowing indirect estimates of soil moisture. Examples of such techniques include evaluating crop water stress, and vegetation anomalies. On the other hand, optical sensors in the thermal spectrum are able to identify temperature differences. The basic principle behind this method is that land surface temperature is sensitive to surface soil water content due to its impact on the surface heating process. The main advantage of these sensors is their ability to provide an estimation with fine spatial resolution, reasonable temporal resolution, adequate accuracy over bare soil and low vegetation cover. Furthermore, these sensors have a long-term free-of-charge image archive and a long-term acquisition plan. However, some drawbacks exist: cloud contamination, lower accuracy over dense vegetation cover, and ability to estimate only top surface soil moisture due to minimal surface penetration. Microwave on the trackMicrowave techniques have proved particularly interesting for the purpose of soil monitoring, because the relative permittivity of land is highly dependent on the moisture content. The amount of water in the soil can thus be estimated by measuring the strength of the signal naturally emitted from the surface (passive sensors), or backscattered from the land surface after transmitting a pulse of microwave energy (active sensors). Traditional passive microwave instruments (also called radiometers) are used to determine surface soil moisture with high accuracy and a temporal resolution of two to three days, but they have a low spatial resolution (around 40 km). In recent years, active microwave sensors (such as Sentinel-1) have been very useful for estimating soil surface characteristics, in particular, soil moisture. With the current Sentinel-1 mission, the SAR sensor onboard offers regular temporal coverage (about 3 days for Europe when both A and B satellites are considered), together with a spatial resolution of up to 10 m. Furthermore, by using active and passive microwave data fusion methods, it could even be possible to retrieve soil moisture at a higher spatial resolution and with higher accuracy. These data can be accessed by everyone through the Copernicus services. Where to find them?If you don’t want to analyse all these data by yourself, near-real time soil moisture information, based on the state-of-the-art “ESA CCI SM” algorithm, can be downloaded from the Copernicus Climate Data Store. There are three products available: the active dataset (based on active scatterometer data), the passive dataset (based on passive radiometer data) or a combined product, based on a combination of both active and passive datasets. When the data is not self-explanatory, you can count on the Copernicus Global Land Service, which is part of the Copernicus Land Monitoring Service. It provides a series of bio-geophysical products that are used to monitor vegetation, water cycle, the energy budget and the terrestrial cryosphere, based on Sentinel-1 data. One of their products, Surface Soil Moisture, shows the relative water content in the top few centimetres of soil (usually up to 5 or 7 cm). The top layer is crucially important, as it provides water supply for vegetation, and directly affects local air temperature and humidity. Copernicus Global Land service, Soil Water Index product over Europe in August 2018 Another useful tool is the Soil Water Index (SWI). It quantifies moisture based on the Surface Soil Moisture, presenting it at various soil depths. The added value comes from combining it with the scatterometer satellite sensor ASCAT on the MetOp EUMETSAT meteorological satellite. It is provided at 1km resolution over Europe, and 0.1 degree, or 12.5 km resolution, at the global scale, on a daily basis, in near-real time. Time series and anomaliesRegular monitoring systems enable multiple applications. For example, it allows to anticipate the impacts of drought on crop production, to estimate availability of water for society and industry, or to spot anomalies. For example, using Copernicus Land’s Soil Water Index (amongst others), the Soil Water Anomaly Drought Index (SWADI) was developed. It is being used by many (e.g. the Indian Council of Agricultural Research) to monitor drought. The index provides real-time monitoring, and a 15-day drought forecast of the impacts of drought on agriculture every 8 days. Similar information about soil moisture anomalies in Europe are also produced by the Copernicus Climate Change Service. Check out the animation below to see monthly soil moisture anomaly for each month in 2018 relative to the average for the same month in 1991-2010. Monthly soil moisture anomaly for each month of 2018 relative to the average for the same month for 1991-2010, as estimated from C3S satellite soil moisture. Data Source: C3S soil moisture v201812 PASSIVE. Credit: Copernicus Climate Change Service (C3S)/ECMWF/TUWIEN/EODC/VanderSat. As we have seen, soil moisture is one of key climate variables. It is helping us understand the current state of our environment and predict potential issues. With a new space-based infrastructure, soil moisture monitoring is currently the most precise and most available it has ever been. All in all, society as a whole can benefit from these crucial data being provided by the Copernicus programme and its services. Don’t miss out on the latest updates from Copernicus. Make sure you are following our social media channels (Twitter, Instagram, and Facebook). |
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来源平台 | The Copernicus Programme |
文献类型 | 新闻 |
条目标识符 | http://119.78.100.173/C666/handle/2XK7JSWQ/275972 |
专题 | 气候变化 |
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