Remote Sensing What is Remote Sensing? Sample Images What do you need for it to work? Electromagnetic Radiation Electromagnetic Spectrum Platforms – Things to consider Satellite Sensors Image Processing Analysis

What is Remote Sensing? "Remote sensing is the science (and to some extent, art) of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information." (CCRS) Aerial Photography – A whole discipline on its own Satellite Imagery – Includes information beyond the visible spectrum. This is what we will focus on.

Advancements http://www.classzone.com/books/earth_science/terc/content/investigations/esu101/esu101page01.cfm

Satellite Orbits Geostationary vs. Near Polar Most satellite we will talk about are Near Polar

Data Collection Passive vs. Active Passive Satellites: Satellites that record reflected and naturally emitted energy from the earth’s surface. (use the sun as energy source) ACTIVE SATELLITES: Satellites that send out their own source of energy to collect data that is not naturally emitted from the earth’s surface. It will record the amount of data reflected back from earth.

This is a true color composite

This is a true color composite

This is a false color composite

This is a false color composite

Why the Strange Colors? Stay tuned to find out!

How does it work? You need some sort of energy source: Naturally, this would be light from the sun. Interaction with atmosphere Object that reflects, absorbs, transmits energy. You need a platform (satellite sensor) that records the reflected electromagnetic radiation. You need a computer that can process the electronic information into an image. You need a computer program and individual who can interpret the images. Read the CCRS website for a detailed tutorial of remote sensing

Electromagnetic Radiation This is the energy source provided by sun. This is the first requirement for remote sensing to work. Energy is emitted from the sun in the form of electromagnetic radiation. Electromagnetic radiation is emitted at various wavelengths. Objects on the earth are sensitive to these different wavelengths. We call this the electromagnetic spectrum. See next slide..

Electromagnetic Spectrum Below is a good picture of the electromagnetic spectrum. You can see examples of objects sensitive to different parts of the spectrum. Notice, the visible part of the spectrum! This is what we see. But look at all of the other information we cannot see at different wavelengths!

Electromagnetic Spectrum Notice how small the visible part of the spectrum is! This is the only part we can associate with the concept of COLOUR. Everything else has “no colour”associated with it. There is a lot of information at different wavelengths and frequencies that we cannot see. This is where remote sensing is so valuable. Violet: 0.4 - 0.446 mm Blue: 0.446 - 0.500 mm Green: 0.500 - 0.578 mm Yellow: 0.578 - 0.592 mm Orange: 0.592 - 0.620 mm Red: 0.620 - 0.7 mm (Wavelength is measured in metres (m) or some factor of metres such as nanometres (nm, 10-9 metres), micrometres (mm, 10-6 metres) (mm, 10-6 metres) or centimetres (cm, 10-2 metres). ) Short Long

So What?…. Remote Sensing deals with the part that is reflected… The electromagnetic radiation hits the earth’s surface. What happens to it when it hits? It can do three things: Remote Sensing deals with the part that is reflected… How much of the electromagnetic radiation is reflected in each wavelength? That is the question…

So What?…. Some things reflect more in parts of the electromagnetic spectrum (or wavelength) then other parts. We call this the object’s spectral signature….at what wavelength does it reflect most? The more familiar you become with this, the more easily you can interpret a remotely sensed image..

What do the satellites do? Sensors record reflectance in each different parts of the spectrum (band) at the same time. A black and white image is created for each band…values of 0-255 assigned. What’s the problem? Technology cannot display all of this information at once!

Image Processing The result is a funny looking colourful image: The more you know about the spectral signatures of features, the more you will understand this image.

Image Processing Computers monitors can only display colours using a combination of red, green and blue dots. These dots of light originate from three “Guns” at the back of the monitor. These guns are called CHANNELS in the remote sensing world. So, we can only display 3 BANDS of information at once by displaying them through the RED, GREEN, or BLUE CHANNEL.

Analysis Band Combinations: True Colour images (land cover detection): Image Red through Red Channel Image Green through Green Channel Image Blue through Blue Channel True Colour False Colour images (vegetation detection): Image Infrared through Red Channel Image Red through Green Channel Image Green through Blue Channel False Colour

Platforms SPOT Landsat (TM) RadarSAT NOAA ERS How do the various satellite platforms use this information? Below are some satellites in the sky right now. Each have different characteristics in terms of spectral, spatial, and temporal resolution. SPOT RADARSAT SPOT Landsat (TM) RadarSAT NOAA ERS LANDSAT ERS NOAA

Spectral Resolution Satellites Image in multiple bands: SPOT XS 20m resolution 0.50-0.59µm - Visible Green 0.61-0.68µm - Visible Red 0.79-0.89µm - Infrared LANDSAT (TM) 30m resolution 0.45-0.52µm Visible Blue 0.52-0.60µm Visible Green 0.63-0.69µm Visible Red 0.76-0.90µm Near Infrared 1.55-1.75µm Mid Infrared 10.5-12.5µm Thermal Infrared 2.08-2.35µm Mid Infrared

Spatial Resolution What size are the pixels? What is the smallest object we can see?

Temporal Resolution How many times does the satellite take an image of the same area? Important for change detection… Don’t forget the satellites orbit and the earth orbits. SPOT – 26 Days LANDSAT – you find out! RADAR – you find out!

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Sources CCRS website Virtual Hawaii website ESRI Canada