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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Thermal-infrared satellites do not see water directly. They measure longwave heat emitted by Earth’s surface and use land-surface temperature, imagery, weather data and models to estimate evapotranspiration (ET) and evaporative stress. Because adequately watered plants usually cool themselves by transpiring, a persistently hot canopy can be an early warning of limited water availability.
Those estimates help farmers, irrigation districts and drought managers see where crops are using water, compare fields and plan investigations. They are not direct readings of irrigation applied, water withdrawn or a guaranteed irrigation prescription; field conditions and other observations are needed to explain what a thermal map means.
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What a thermal-infrared satellite actually measures
Every surface emits longwave infrared energy. The intensity and wavelength distribution of that energy are related to the surface’s temperature and emissivity. A thermal-infrared instrument detects that emitted energy and processes it into a land-surface-temperature estimate. It is measuring heat, not soil moisture, irrigation volume or plant water content.
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NASA’s Thermal Infrared Sensor (TIRS) on Landsat measures land-surface temperature in two thermal bands. Those observations are useful to water-resource managers tracking land and water use. NASA notes that nearly 80 percent of fresh water in the Western United States is used for crop irrigation; that figure is specific to the Western U.S. and should not be generalized to every region or all water uses.
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Why temperature changes when plants run short of water
Plants move water from roots to leaves and release some of it through tiny pores called stomata. That process, transpiration, consumes energy and cools leaves and the surrounding canopy. Soil and open-water surfaces also lose water through evaporation. Together, evaporation and transpiration are called evapotranspiration.
When water is available, evaporative cooling can keep a crop canopy relatively cool. As water becomes limiting, plants may close their stomata to slow water loss. Cooling then weakens and canopy or soil temperatures can rise. A temperature anomaly can therefore signal stress before a crop shows obvious wilting, but it is not proof of a particular cause. Bare soil, wind, humidity, crop age, disease, salinity and heat waves can also change the temperature a sensor sees.
How temperature becomes an evapotranspiration estimate
ET is the amount of water transferred from soil, plant and other land surfaces to the atmosphere over a period of time. Satellites do not measure that transfer directly from a single thermal image. Scientists combine thermal observations with visible and near-infrared imagery, vegetation information, weather observations, radiation estimates, terrain and model assumptions.
- Measure emitted heat. A thermal instrument records longwave radiation and algorithms estimate land-surface temperature while accounting for atmospheric effects and surface emissivity.
- Describe the vegetation and surface. Reflective satellite bands help identify crop cover, canopy density, bare soil and field boundaries. Weather and radiation data describe the energy available for evaporation.
- Estimate energy used by evaporation. Models partition the surface energy budget among sensible heat, ground heat and latent heat associated with ET. A cooler, actively transpiring canopy generally receives a larger evaporative component than a dry, hot surface.
- Scale observations through time. A satellite sees a field only at observation times. Models and meteorological inputs extend the information between images and produce daily, weekly or seasonal ET layers, depending on the product.
- Derive stress indicators. Comparing estimated ET with a reference demand, potential ET or expected crop behavior can produce an evaporative-stress indicator. The result is an analytical estimate, not a direct sensor reading of plant stress.
NASA’s explanation in “Evapotranspiration: Watching Over Water Use” describes ET as a way to estimate water consumed by crops and other vegetation. Research scientist and ECOSTRESS principal investigator Simon Hook summarized the value as: “By measuring evapotranspiration, we get an early indicator of what plants are experiencing.”
ECOSTRESS, Landsat TIRS and OpenET: related but different
These systems are often discussed together because they all support temperature, ET or water-use analysis. They are not interchangeable products. The right choice depends on the geography, field size, update timing and decision being made.
| System or service | What it measures or derives | Coverage and access | Best-fit decisions |
|---|---|---|---|
| Landsat TIRS | Land-surface temperature in two thermal infrared bands, combined with other Landsat observations for agricultural and water studies. | Landsat observations feed many analysis workflows; NASA provides instrument information at its TIRS overview. | Field and landscape temperature patterns, land-use and water-resource monitoring, and inputs to ET models. |
| ECOSTRESS | Surface temperature and products supporting ET and evaporative-stress analysis. NASA describes the mission as monitoring water loss through plant leaves. | Data are distributed through NASA Earthdata, the LP DAAC and AppEEARS; see ECOSTRESS Data. | Drought, crop and ecosystem stress studies that benefit from observations at different times of day. |
| OpenET | Field-level ET estimates generated from Landsat thermal data, other imagery and multiple model methods. | NASA describes it as an open-source platform covering the contiguous United States. See NASA’s Agriculture & Food Security overview. | Estimating crop water consumption, comparing fields and supporting irrigation-efficiency and water-accounting work. |
NASA’s ECOSTRESS science page reports that more than half a million scenes had been acquired by January 2025. That count indicates the scale of the archive, not that every location has continuous coverage or that all scenes are suitable for a particular farm.
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ECOSTRESS sampling details need a date
A NASA/JPL webinar page dated March 25, 2019 described ECOSTRESS products at 70-meter resolution and repeat visits over a location approximately every three to five days, with observations occurring at different local times because the instrument is on the International Space Station. Those figures describe that dated mission presentation. Users should check current product documentation before treating them as present-day operational specifications.
What a drought or crop-stress workflow looks like
A useful monitoring program treats the thermal layer as one part of a repeatable decision process rather than as a stand-alone diagnosis.
1. Define the decision and area
Specify whether the question concerns a single field, an irrigation district, a watershed or a regional drought. Also define the time window: an irrigation event, a growing season, a month or a multi-year anomaly. Field-level irrigation scheduling requires finer spatial detail and more frequent information than regional drought screening.
2. Obtain imagery and quality information
Download suitable Landsat or ECOSTRESS scenes, or use an ET service such as OpenET where coverage applies. Check acquisition date, cloud and shadow masks, sensor quality flags, field boundaries and whether the scene was collected before or after an irrigation event. A cloudy or contaminated pixel can produce a misleading temperature or ET value.
3. Compare temperature with crop and weather context
Map hot and cool areas alongside crop type, planting date, canopy development, soil texture, elevation, wind, humidity and recent rainfall. Compare a field with nearby fields of the same crop and growth stage rather than using a single universal temperature threshold.
4. Examine ET over time
Use a time series to distinguish a short-lived hot observation from a persistent decline in estimated ET. A single afternoon can reflect heat, wind or a recent harvest; repeated departures from expected ET are more informative for drought and irrigation investigations.
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5. Investigate on the ground
Walk or sample locations where temperature and ET differ from neighboring fields. Check emitters, valves, pumps, irrigation timing, soil moisture, salinity, pests, disease, compaction and crop uniformity. The field visit is where a satellite signal becomes an operational explanation.
6. Record the decision and uncertainty
Document the product, date, model, quality flags, weather conditions and any irrigation or rainfall observations used. Preserve the distinction between an estimated ET deficit, an irrigation recommendation and the amount of water actually applied.
How to interpret an ET map without confusing it with irrigation
ET describes water transferred to the atmosphere. Irrigation applied is water delivered by a system. Water withdrawal is what a canal, well or reservoir supplies. These quantities can differ because of rainfall, runoff, deep percolation, conveyance losses, soil storage and changes in crop demand.
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| Quantity | Meaning | What a satellite-based product can support |
|---|---|---|
| Land-surface temperature | Estimated heat state of the surface or canopy at observation time. | Locate thermal anomalies and compare patterns after quality screening. |
| Evapotranspiration (ET) | Estimated evaporation plus plant transpiration over a time period. | Estimate crop water consumption, compare fields and assess seasonal water use. |
| Evaporative stress | An indicator derived by comparing observed or modeled ET with expected atmospheric demand or crop behavior. | Flag areas for drought or irrigation investigation. |
| Irrigation applied | Volume delivered to a field by a sprinkler, drip, flood or other system. | Not directly measured by thermal imagery; verify with meters, system records or flow estimates. |
| Water withdrawal | Water taken from a river, canal, reservoir or aquifer. | Requires accounting data and infrastructure measurements beyond a thermal map. |
An ET deficit can indicate that a crop is receiving less water than expected, but it does not state how many millimeters to apply. Turning an estimate into an irrigation decision requires crop stage, rooting depth, soil water, forecast weather, system efficiency and local agronomic guidance.
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Field irrigation management
Repeated temperature and ET layers can reveal a dry corner, clogged irrigation zone or uneven crop development that average field totals hide. Comparing adjacent fields can help prioritize scouting and maintenance. The signal is most useful when field boundaries, crop type and irrigation records are accurate.
Drought early warning
Regional agencies can combine persistent ET reductions with rainfall deficits, reservoir conditions, streamflow, vegetation indices and weather reanalysis. Thermal stress may appear before visual damage, allowing managers to target inspections or assistance. It should not replace precipitation, soil-moisture or hydrologic indicators.
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- 【Multi-Scenario Application】It supports a broad measurement range from -4°F to 1022°F with enhanced with adjustable emissivity and distance settings,making it suitable for applications.Equipped with a high-sensitivity sensor (NETD < 50mK), the thermal camera can detect extremely subtle temperature differences as small as 0.05°C.
- 【Quick Anomaly Detection with Alerts 】Featuring a 50° wide field of view, the device enables faster scanning of large surfaces and broader inspection coverage. It supports custom high/low temperature alarms for instant notification when abnormal thermal conditions are detected. Level and span adjustment functions make it easier to clearly identify localized issues.
- 【All-Day Battery Life】Built-in 2500mAh rechargeable battery provides up to 14 hours of continuous operation, supporting full-day inspection without frequent recharging. The device also includes a 1-year warranty, ensuring long-term reliability and peace of mind for using.
Water accounting and efficiency
Field-level ET estimates can support estimates of consumptive use and comparisons among irrigation practices. OpenET is designed to provide field-level ET information across the contiguous United States and to support water-consumption and irrigation-efficiency analysis. Its estimates still depend on model inputs and quality control; they are not a meter installed at the field inlet.
Ecosystem and heat studies
ECOSTRESS observations can show how vegetation responds at different times of day, which is useful for studying daily water use and heat exposure. NASA’s ECOSTRESS applications material discusses agriculture and drought monitoring, while the mission science page explains that the instrument monitors water loss through leaf pores. Access routes and product definitions are listed on the ECOSTRESS Applications and ECOSTRESS Research pages.
Common reasons a hot or low-ET pixel can mislead
- Atmospheric contamination: clouds, haze and cloud shadows can distort or invalidate thermal retrievals.
- Mixed pixels: at the edge of a field, one pixel may contain crop, bare soil, roads or trees, so its temperature is not a pure canopy measurement.
- Different crop stages: a young or recently harvested field naturally transpires less than a full canopy and may appear hotter.
- Weather effects: wind, humidity and incoming radiation alter evaporative demand and surface temperature even when soil water is unchanged.
- Non-water stress: salinity, disease, insects, nutrient shortages, compaction and mechanical damage can reduce transpiration or change canopy temperature.
- Timing: an image collected soon after irrigation may look different from one collected before irrigation; compare observations with event records.
- Model uncertainty: ET products use assumptions and multiple inputs. Different models can produce different estimates, especially where observations are sparse or conditions are unusual.
Choosing information for a particular job
There is no universally superior satellite or product. Use the following fit test before selecting a workflow:
- Need a temperature snapshot? Start with a quality-screened thermal product and interpret it with crop and weather layers.
- Need field-level water consumption in the contiguous U.S.? OpenET’s Landsat-based, modelled ET layers are designed for that context.
- Need observations at varied times of day or ecosystem-scale stress analysis? Investigate ECOSTRESS products and their current access documentation.
- Need a decision outside the named coverage? Confirm geography, product availability and local validation before assuming that a U.S.-focused service or a particular revisit interval applies.
- Need an irrigation prescription? Combine ET and stress indicators with soil-moisture measurements, crop coefficients, weather forecasts, irrigation-system data and an agronomist or water manager’s judgment.
Accessing the data
NASA’s ECOSTRESS data page identifies NASA Earthdata, the Land Processes Distributed Active Archive Center (LP DAAC) and AppEEARS as access routes. Product users should read the current collection documentation, including spatial resolution, quality flags, latency, processing level, units and licensing.
For Landsat applications, NASA’s Landsat agriculture fact sheet and its Agriculture & Food Security overview describe how thermal observations and other imagery support agricultural monitoring. OpenET availability is described for the contiguous United States; do not infer global coverage from that description.
The practical bottom line for managers
Thermal-infrared satellites provide a scalable way to see where land is hotter or cooler and where estimated ET is diverging from expected crop water use. That makes them valuable for prioritizing field visits, tracking drought development, comparing irrigation performance and informing water accounts. Their value comes from combining repeat observations with weather, crop, soil and operational records.
The safe interpretation is “this area warrants attention,” not “the satellite measured the irrigation” or “apply this exact amount.” Treat temperature and ET as evidence in a broader water-management system, preserve the product’s date and uncertainty, and verify important decisions with field measurements.
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