What Is Remote Sensing? - Definition, Applications & Example

Instructor: Bob Bruner

Bob is a software professional with 24 years in the industry. He has a bachelor's degree in Geology, and also has extensive experience in the Oil and Gas industry.

Hypotheses about physical systems are modified based on the results of scientific tests and observations. Remote sensing capabilities have significantly increased our ability to gather data that is not immediately apparent from our own personal senses.

Enhancing our Senses

Human beings use their senses in order to interact directly with the environment. We can see, hear, touch, taste and smell the various stimuli around us, and we then process that information using our brains. Other animals often make use of sensory capabilities not available to humans. Echolocation by flying bats and electrical field detection by swimming sharks are but two of a vast range of sensory perceptions that lie outside human capability. Even our pet dogs hear better than we do, in part because they can detect frequencies of sound not perceived by the human ear.

Humans, however, have learned how to 'see' inside the earth and detect features hidden from our senses, not only on our earth but also across the vast reaches of the universe. For these and many other purposes, we typically make use of remote sensing.

Definition and Characteristics

Remote sensing is defined as any process by which we observe the physical attributes of a system using remotely located sensing devices. This definition is fairly broad and encompasses many different technologies. In general, however, the term is most often used in reference to observations made of the earth's surface and its interior using sensors placed on aircraft, drones, or satellites.

Two basic categories of remote sensing are recognized, based on whether the input data is passive or active. A passive signal is one that is naturally occurring, and only requires us to have the right equipment located in the right place to take measurements. In contrast, an active system is one that generates its own energy and then records the returned signals.

These signals span a broad range of electromagnetic frequencies. Radio waves, microwaves, and infrared waves are the most common signals used in remote sensing. These longer wavelengths are able to penetrate through clouds and other atmospheric layers, and are less attenuated over longer distances.

Because remote sensing devices often operate outside the visible light spectrum, some form of data processing is also typically required in order for humans to be able to interpret the data. Data processing techniques are particularly useful in uncovering and highlighting details that might otherwise remain hidden in the data.

Remote Sensing in Action

One of the oldest satellite-based earth monitoring systems is the Landsat program, administered by the U.S. government. This program has been in operation since the early 1970's, and maintains a vast catalogue of historical reference data that is still being updated today.

Tracking Deforestation

The amount and rates of deforestation over time have been actively monitored by the Landsat project. Simple photographic images have been used to compare vegetative cover over time. In addition, near infrared images taken from satellites are particularly useful in showing areas of vegetation, as the chlorophyll found in leaves reflects most of the energy in this electromagnetic range.

Detecting Ground Water

Infrared images are also useful in detecting the presence of water, even if it is already absorbed into the earth. Three very specific narrow bands of infrared signals are readily absorbed by water molecules. When looking at images using only these specific bands, any ground water and any water-saturated soil will appear as dark features on the processed image. One of the most recent trends in agriculture is to use these satellite images, or images taken from drone flyovers, to locate exactly where additional irrigation is required in an area of cropland. This type of precision agriculture is an important method by which water conservation can be greatly enhanced using remote sensing.

Weather Forecasting

We can also very accurately map the presence of water vapor in the atmosphere using somewhat longer infrared signals. Water vapor typically only accounts for 2 or 3 percent of the earth's atmosphere, and can only be seen in visible light if it accumulates into cloud cover. However, even a small amount of water vapor will absorb and re-emit energy in the 6000-7000 nanometer wavelength. This satellite data is an integral component of improved weather forecast models.

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