Earth in focus

We have been observing Earth from space for many years. Over this time, the technologies used to do so have changed dramatically. The very first picture of Earth from space was taken on October 24th, 1946 from a rocket 105 km above the ground. The rocket, from World War II, had the warhead replaced with a package of scientific instruments including a 35 mm motion-picture camera that was set to snap a picture every 90 seconds. The images were dropped back to Earth in a tough steel canister.

Our technologies and capabilities have certainly improved since the first picture was taken. The iconic “The blue marble” taken by astronauts aboard the Apollo 17 in 1972 was the first full view of the Earth and was taken while Apollo was on its way to the moon. In more recent times, satellites a little closer to Earth, about 824 km up, take composite images of Earth allowing for more detail, taking pictures as they repeatedly orbit the Earth. Since the first satellite was launched in 1957, many have been sent into space to collect data about the Earth. We have progressed from only being able to take photographs of Earth to collecting complex information such as temperature, concentrations of atmospheric gases, exact elevations of land and sea levels, and much more.

Remote sensing refers to the collection of data from a distance. Many different types of sensors, on different types of platforms, can be used to observe the Earth from above. Types of platforms that are used to perform Earth observation include drones, airplanes, stratospheric balloons, and satellites. The term “remote sensing” is most often used to imply Earth observation from a satellite.

The first Earth observation satellite was a weather satellite called TIROS 1 (Television Infrared Observation Satellite). It was launched by NASA in 1960 and equipped with cameras to take images of Earth’s atmosphere. This led to the development of real-time video surveillance for other purposes, such as geographic observation and military intelligence. Later, the first satellite devoted to monitoring land – Landsat 1 – was launched by NASA in 1972.

Later, the first satellite devoted to monitoring land – Landsat 1 – was launched by NASA in 1972.

Earth observation (or EO) is the term given to the collection of information about our Earth systems via remote-sensing technologies. EO can include both space-based as well as ground or air-based data.

Canada launched its own Earth Observation (EO) satellite, RADARSAT-1, in 1995 followed by its successor, RADARSAT-2 in 2007. In 2019, the RADARSAT Constellation Mission (RCM) was launched. It consists of three identical satellites that work together to observe Earth as never before. RCM is designed to provide effective solutions in three main areas: maritime surveillance (ice, surface wind, oil pollution and ship monitoring), disaster management (mitigation, warning, response and recovery), and ecosystem monitoring (agriculture, wetlands, forestry and coastal change monitoring.)

Scientists have been asking questions about Earth’s systems and collecting data from satellites to study Earth’s changing environment for many years.  Engineers help design instruments to get the measurements needed to help answer scientists’ questions, giving us a variety of instruments used to get the big picture of our Earth system.

As was already mentioned, different sensors are used to observe the Earth. Satellites orbiting the Earth carry sensors that measure data using different sections of the electromagnetic spectrum.

Electromagnetic energy travels in waves and spans a broad range, from very long radio waves to very short gamma and cosmic rays. Humans can see only a small portion of the spectrum – this portion is called visible light and is what astronauts and their cameras would observe. Satellites use a broad range of the spectrum to study the Earth. Remote sensing of Earth most frequently uses energy in the visible, infrared (IR), and microwave portions of the spectrum.

• Gamma rays or Cosmic rays: are not used to study the universe.
• X-rays: are used to photograph and study the sun.
• Visible light: is used to take true colour images of the Earth and its features.
• Infrared: is used to view and track hurricane paths, since it is not affected by cloud cover, and for measurements of the Earth’s land and sea surface temperatures.
• The microwave portion of the spectrum is the most useful for Earth observation remote sensing.
  • Microwave instruments are able to sense much longer wavelengths
  • Microwaves are able to penetrate clouds which can completely block a satellite’s view in the visible and infrared spectrums
  • They are used to observe clouds, precipitation, and water vapour, monitor land and sea surfaces and perform atmospheric profiling of temperature and humidity.
• Radio waves have the longest wavelength and lowest frequency. RF sensors can provide continuous coverage, day and night, irrespective of the cloud coverage. RF remote sensing provides data on weather forecasts, climate change, and disaster management among others.

Supplemental information

Satellites can include active or passive sensors.

• Passive sensors detect natural energy that is emitted (released) or reflected by the object that is being observed. (For Earth observation sunlight would be the most common source of energy being measured by passive sensors.)
• Active sensors provide their own source of energy to illuminate the objects they observe. The sensor will detect and measure the energy that is reflected back from the target. Different sensors are equipped to measure different parts of the electromagnetic spectrum. For example, our eyes (passive sensors) can only detect wavelengths that are part of the visible spectrum (the colours of the rainbow) but some satellite sensors can also detect ultraviolet and infrared light among others.

Learning objective

To demonstrate to students how it can be difficult to interpret an image of Earth from space.

Introduction

In recent years, the general public has been lucky to have much more access to photos from space and satellite images. Google Earth and space agencies around the world provide us with images of Earth from space. We can see how cities are changing, the effects of storms in far away places or at home, and even see how crops are growing. Really understanding the images though isn’t always as easy as it may seem. Sometimes, without proper context, our eyes can play tricks on us!

Check out the printable PDF at the bottom of the page for more info!

Astronauts can be disoriented in space especially at the beginning of their mission. For this reason, they are trained extensively to be able to orient themselves relative to Earth and to identify features. Knowing how to look at the Earth also provides them with an important psychological advantage of remaining connected to home. During their training astronauts are reminded that what they will be recording will be used for scientific purposes and will contribute to research being done around the world.

There are some key tips to help us make sense of what we are seeing.

3. Define the colours

The colour in images will depend on what kind of light the satellite instrument measured.  True-colour images use visible light and are similar to what you would see from space.  False-colour images incorporate infrared light and may take on unexpected colours – since infrared light is ‘invisible’ to human eyes these types of light are assigned visible colours to represent them. In a true colour image plants are usually different shades of green but land used for agriculture may often be much brighter than natural vegetation.  Sunlight reflecting off water makes it look gray, silver or white.

It would be very difficult to tell what you were looking at in the above image without a guide to show you the meaning of the colours.

4. Find north

Try to figure out what you are looking at by identifying features and whether other features are north or south of that etc.

5. Consider your own knowledge

This is probably the most helpful in identifying key features and requires lifelong learning and practice.

Instructions

There are many ways to direct this activity and adjustments can be made by age:

1. The activities are on the accompanying slides and can be projected to be completed as a class activity.
2. Students can be assigned the activities online through Google Forms.
3. Questions can be printed and students can work alone or in groups.
4. Images can be used for many different types of activities: describe the image; identify features in the image; etc.

Go further!

• For older students, satellite images can be used to determine distances between features. Instructions to do so can be found on the Natural Resources Canada website.
  • Measure This (Northern Saskatchewan)
• Landsat science NASA resources