Mapping the Invisible: Introduction to Spectral Remote Sensing

Summary

This script explains the concept of spectral remote sensing, which involves measuring properties of objects using reflected light energy across the electromagnetic spectrum. It distinguishes between regular cameras that capture visible light and imaging spectrometers that record both visible and non-visible light, aiding in environmental monitoring. The script details how spectral signatures, influenced by an object's chemical and physical properties, enable scientists to identify and map different surfaces and objects, such as vegetation, using multi and hyperspectral data.

Takeaways

• 📷 Spectral remote sensing involves measuring properties of objects using light from the electromagnetic spectrum, including both visible and invisible light.
• 🌐 A typical camera captures visible light reflected by objects, while imaging spectrometers are used by scientists to measure more detailed environmental changes.
• 🌳 Imaging spectrometers mounted on aircraft and satellites help create detailed maps, such as vegetation cover across the United States.
• 🌈 The electromagnetic spectrum is composed of thousands of wavelengths, with visible light being just a small part of it.
• 🔍 Imaging spectrometers divide the spectrum into specific groups of wavelengths called bands, which are used to detect different features of the environment.
• 🌿 Different objects have unique spectral signatures based on how they reflect, absorb, and transmit light, which is influenced by their chemical and structural properties.
• 🐕 Examples like plant leaves reflecting more green light and a dog reflecting more red light illustrate how spectral signatures vary between objects.
• 🖼️ RGB images are created from the red, green, and blue bands of the electromagnetic spectrum, with each pixel representing a combination of these colors.
• 📊 Spectral signatures can be plotted to show the amount of energy reflected at different wavelengths, helping to distinguish between different types of surfaces and objects.
• 🌱 Multi and hyperspectral remote sensing data, recorded by imaging spectrometers, allow for the measurement of light in both visible and non-visible parts of the spectrum, aiding in environmental monitoring.

Q & A

What is spectral remote sensing?

Spectral remote sensing involves measuring the properties of objects without directly touching them by capturing both visible and invisible light within the electromagnetic spectrum.

How do imaging spectrometers differ from typical cameras?

Imaging spectrometers are high-powered cameras that measure changes in environmental factors like water quality or vegetation cover and health, using both visible and non-visible light in the electromagnetic spectrum.

What is the significance of the electromagnetic spectrum in remote sensing?

The electromagnetic spectrum is crucial in remote sensing as it contains thousands of wavelengths of energy that can be detected and recorded to analyze the properties of objects on Earth's surface.

What is the role of spectral resolution in imaging spectrometers?

Spectral resolution refers to the width and number of bands in the spectrum that an imaging spectrometer can capture. Higher spectral resolution means more, spectrally narrow bands, allowing for more detailed analysis.

Why are different objects' spectral signatures important in remote sensing?

Different objects' spectral signatures are important because they represent the unique physical and chemical properties of the objects, which can be used to identify and classify them in remote sensing imagery.

How does the color of an object, like a plant leaf, relate to its spectral signature?

The color of an object, such as a plant leaf being green, is due to its reflection of more green light than blue or red light, which is reflected in its spectral signature as a higher intensity in the green band of the spectrum.

What is an RGB image and how is it created?

An RGB image is a color image created by combining red, green, and blue light bands. Each pixel in the image contains values representing the amount of red, green, and blue light reflected, forming a composite image.

How do imaging spectrometers capture multi and hyperspectral data?

Imaging spectrometers capture multi and hyperspectral data by recording light in many narrow bands across both visible and non-visible parts of the electromagnetic spectrum, providing detailed information about the objects' properties.

What is the practical application of spectral signatures in mapping vegetation?

Spectral signatures are used in mapping vegetation by identifying areas with high near-infrared light reflection, which is a characteristic of healthy vegetation, allowing for detailed vegetation cover maps.

How can spectral remote sensing help measure changes in the environment?

Spectral remote sensing helps measure changes in the environment by analyzing the spectral signatures of objects over time, detecting variations in properties such as water quality, vegetation health, and land use changes.

Outlines

00:00

📸 Understanding Spectral Remote Sensing

This paragraph introduces the concept of spectral remote sensing, which involves measuring the properties of objects without direct contact by capturing light across the electromagnetic spectrum. It explains how typical cameras capture visible light reflected by objects, while imaging spectrometers used by scientists measure changes in environmental factors such as water quality and vegetation health. The paragraph also delves into the electromagnetic spectrum, detailing how imaging spectrometers divide it into specific bands to measure reflected light energy. The concept of spectral resolution and how different objects reflect light differently based on their chemical and structural properties are discussed. The paragraph concludes with an explanation of how cameras create RGB images and spectral signatures, which are used to differentiate between various objects and surfaces.

05:05

🌿 Applications of Spectral Signatures in Environmental Mapping

The second paragraph focuses on the practical applications of spectral signatures in identifying and mapping objects on Earth's surface. It emphasizes how imaging spectrometers record the amount of light reflected by objects across the electromagnetic spectrum, creating unique spectral signatures that are influenced by the object's physical structure and chemical composition. These signatures are crucial for differentiating between various objects in photographs and across the Earth's surface. The paragraph highlights the importance of spectral signatures in environmental monitoring, such as mapping vegetation and measuring changes in the environment. It concludes by summarizing the process of using reflected light energy to map the Earth's surface and track environmental changes.

Keywords

💡Spectral Remote Sensing

Spectral remote sensing refers to the technique of capturing and analyzing data across various wavelengths of the electromagnetic spectrum, including both visible and invisible light to the human eye. This technology is crucial for the video's theme as it allows scientists to measure properties of objects without direct contact, which is essential for environmental monitoring. The script mentions how imaging spectrometers, a type of high-powered camera, are used for this purpose, capturing changes in environmental factors like water quality and vegetation health.

💡Electromagnetic Spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation, which includes visible light, radio waves, X-rays, and more. In the context of the video, the spectrum is highlighted as being composed of thousands of wavelengths of energy, each with unique properties. The script explains how different parts of the spectrum, such as the visible light (blue, green, and red) and the near-infrared, are used to detect and analyze various features of the environment.

💡Imaging Spectrometers

Imaging spectrometers are advanced camera-like devices that can measure and record light across a broad spectrum of wavelengths. They are a key technology in the video's discussion of environmental monitoring. The script describes how these devices are mounted on airplanes and satellites to create detailed maps of vegetation cover and other environmental features. They are capable of capturing both visible and non-visible light, which is essential for detailed spectral analysis.

💡Spectral Resolution

Spectral resolution refers to the ability of an imaging instrument to distinguish between two close spectral lines or to the width of the wavelength bands it measures. The higher the spectral resolution, the more detailed the information that can be obtained. The video script uses the term to explain how imaging spectrometers divide the spectrum into narrow bands to capture detailed data about the reflected light energy from objects, which is vital for creating accurate environmental maps.

💡RGB Image

An RGB image is a digital image composed of the three primary colors: red, green, and blue. Each pixel in an RGB image contains a value for each of these colors, which combine to create the full range of colors seen in the image. The video script explains how a typical camera records light in these three bands to create an image, and how these bands can be analyzed separately to understand the amount of light reflected by objects in each color spectrum.

💡Spectral Signature

A spectral signature is a unique pattern of reflected light that an object exhibits across the electromagnetic spectrum. It is determined by the physical and chemical properties of the object. In the video, spectral signatures are used to differentiate between various surfaces and objects, such as vegetation and animals, by analyzing the specific wavelengths of light they reflect. This concept is central to the video's message about how reflected light energy can be used to identify and map objects on Earth's surface.

💡Vegetation Cover

Vegetation cover refers to the extent of an area covered by plants and trees. In the video, the term is used in the context of creating maps of vegetation using imaging spectrometers. These maps are important for understanding environmental health and changes over time. The script mentions how plants reflect a significant amount of light in the near-infrared portion of the spectrum, which is crucial for accurately mapping vegetation.

💡Multispectral and Hyperspectral Remote Sensing

Multispectral remote sensing involves the use of multiple, broad bands of the electromagnetic spectrum, while hyperspectral remote sensing uses hundreds of narrow bands at high spectral resolution. Both techniques are discussed in the video as methods for capturing detailed data about the Earth's surface. The script explains that these data sets allow scientists to measure light energy reflected from objects and estimate their physical and chemical properties, which is invaluable for environmental analysis.

💡NIR (Near-Infrared)

Near-infrared (NIR) is a part of the electromagnetic spectrum that is adjacent to the visible light spectrum. It is not visible to the human eye but can be detected by imaging spectrometers. The video script highlights the importance of NIR in remote sensing, particularly for mapping vegetation, as plants reflect a significant amount of light in this region compared to visible light. This property is used to differentiate vegetation from other surfaces in the environment.

💡Physical and Chemical Properties

Physical and chemical properties refer to the characteristics of matter that determine its behavior and interactions. In the context of the video, these properties are important because they influence how objects reflect, absorb, and transmit light. The script explains that the spectral signature of an object, which is captured by imaging spectrometers, is driven by its physical structure and chemical makeup. Understanding these properties is key to identifying and classifying different objects and surfaces on Earth's surface.

Highlights

Spectral remote sensing involves measuring properties of objects without direct contact using the electromagnetic spectrum.

Cameras measure visible light reflected by objects, but imaging spectrometers measure changes impacting the environment like water quality or vegetation health.

Imaging spectrometers mounted on airplanes and satellites help create detailed maps like the vegetation cover map for the United States.

The electromagnetic spectrum is composed of thousands of wavelengths, including visible light and other forms of energy.

Imaging spectrometers divide the spectrum into groups of wavelengths called bands to manage the vast amount of data.

Spectral resolution refers to the width and number of bands, with higher resolution indicating more narrow and numerous bands.

Different objects have unique ways of reflecting, absorbing, and transmitting light based on their chemical and structural properties.

RGB images are created by cameras, which record the amount of red, green, and blue light reflected from objects.

Spectral signatures plot the amount of energy reflected at specific wavelengths, helping to differentiate between objects.

Plants reflect significantly more light in the near-infrared spectrum, which is crucial for vegetation mapping.

Imaging spectrometers record both visible and non-visible light, producing multi and hyperspectral data for detailed analysis.

Multispectral data consists of many bands, while hyperspectral data can have hundreds of bands at high spectral resolution.

These data sets are used to estimate physical and chemical properties of objects on Earth's surface that are not visible to the naked eye.

Spectral signatures, driven by an object's physical structure and chemical makeup, are used to identify and classify objects on the ground.

Reflected light energy and spectral signatures are essential tools for mapping the Earth's surface and measuring environmental changes.

Transcripts

If you've ever used a camera then you know something about spectral remote sensing.

"Spectral" related to the electromagnetic spectrum which includes light that is

both visible and invisible to human eyes and "remote sensing" which involves

measuring the properties of objects without directly touching them.

The typical camera that you use measures and records visible light that objects like

trees and rock reflect. This light might come from the Sun but it also might come from

other sources like light bulbs.

While we often use cameras to take selfies and silly pictures of our furry friends,

scientists use high-powered camera is called imaging spectrometers to measure

changes in things that impact our environment like water quality or

vegetation cover and health.

Imaging spectrometers mounted on airplanes and satellites

help us create maps like this vegetation cover map for the entire

United States. But how exactly do scientists measure changes to our

environment using reflected light energy?

To answer this question, let's have a look at the electromagnetic spectrum

which is composed of thousands of wavelengths of energy.

Visible light, what we see with our eyes, is contained in the

blue, green, and red portions of the spectrum. The rest of the spectrum is not

visible to humanize but can be detected and recorded by sophisticated camera

like sensors called imaging spectrometers.

Now there are thousands of wavelengths to record in the electromagnetic spectrum.

To deal with all these wavelengths, imaging spectrometer is

divided the spectrum into groups of wavelengths called bands.

For example, a band in the near infrared region of the spectrum could include energy from 800 to

850 nanometers. This band is useful to map healthy vegetation.

The width and number of bands is what we call the spectral resolution of an image.

Higher spectral resolution means more bands that are spectrally more narrow.

Lower spectral resolution means fewer bands, each of which covers more of the spectrum

Now imaging spectrometers measure reflected light energy.

You see different objects reflect, absorb, and transmitted light differently

depending on their chemical and structural characteristics.

For example, plant leaves are green because they reflect more green light than blue or red light.

On the other hand, Fido the Dog reflects more light in the red portion of the spectrum

because of the chemical and structural makeup of his fur. If Fido's chemical and

structural makeup was the same as a plant then he would look green.

Now when you point your camera toward your favorite canine doing something silly

the camera record the amount of light reflected from the dog and its surroundings

in the visible, or red, green, and blue bands of the electromagnetic spectrum.

The camera creates what's called an RGB image which is composed of millions of pixels.

Each pixel in the image contains a value representing the amount of red, green, and blue light reflected.

We can break the image out into its red green and blue bands too.

Here's the red band on its own.

Brighter pixels mean that more light was reflected by objects in the image and

recorded by the camera in the red part of the electromagnetic spectrum.

The darker parts are areas where less light was recorded. When we combine the red

green and blue bands together we get an image that looks similar to what we see

through the camera lens.

We can plot the amount of red green and blue light

recorded in each pixel to create what's called a spectral signature.

In the signature the amount of energy reflected in a particular wavelength as shown in

the y axis and the full range of wavelengths that were measured by the

camera, in this case blue, green, and red, is on the x-axis. The spectral signature for

Fido is quite different from the spectral signature for our plant this

makes them appear visually different to our eyes too.

Differences and spectral signatures can help scientists identify different types of surfaces and objects within images.

Most cameras record light in the visible or red, green, and, blue bands,

however, plants, dogs, and other objects on the earth also reflect light that we can't see with our eyes.

For example plants reflect up to sixty percent more

light in the near infrared portion of the electromagnetic spectrum than they

do in the green portion of the spectrum.

This is why differences in the reflected light in the near infrared portion of

the spectrum are important for mapping vegetation on the ground.

To measure these differences in the non visible portion of the spectrum we use

imaging spectrometers, which record light in both visible and non visible parts of

the spectrum. Imaging spectrometers produced what are called multi and hyperspectral remote sensing data.

"Multi" meaning many bands, more than three, and

"hyper" meeting up to hundreds of bands clicked at very high spectral resolution.

We use these multi and hyperspectral remote sensing data sets

to measure light energy reflected from objects on the Earth's surface

and to estimate many physical and chemical properties

of objects that we wouldn't see with our own eyes.

We then uses measurements to classify what's on the ground.

For example, pixels that have a spectral signature with a lot of near-infrared light energy are often vegetation.

To review, different objects reflect, absorb, and transmit

both visible light and light energy that we can't see differently.

Imaging spectrometers record the amount of light that these objects reflect.

The amount of light energy reflected by an object throughout the electromagnetic spectrum

is called its spectral signature which is driven by the physical structure and

chemical makeup of the object. We can use that signature to identify different

objects in both a photograph and across the Earth's surface.

And that my friends, is how we use reflected light energy to both map what's on the ground

and measure changes in our environments.