Topic 1a - The early days of optical EO

Welcome to the first topic of the course. For each new topic you should watch the main video (above), read the explanatory text (below), and you can find links to optional further reading at the external websites in the ‘See Also’ section at the bottom of the page. You can also find more information about the data, imagery, animations and satellite missions featured in each topic in the step that follows each video.

Remote sensing is the sensing of anything without direct contact – so your own eyes are a remote sensing instrument. Remote sensing allows for a whole range of science depending on how much detail we can see, how often we can take measurements, and what kind of measurements we can take. It covers a whole range of applications than we will cover here, such as photography, astronomy including the study of planets and exoplanets, and so on. Earth observation (EO) is a more specific term, implying remote sensing of the Earth and its various components, including of course the human element – our impact on and place within that system. EO covers remote sensing including the gathering of physical, chemical, and biological information about our planet, and grew out of humankind’s innate desire to understand the world better. Earth observation uses indirect measurement of electromagnetic (EM) radiation, along the spectrum from ultraviolet to radio waves (using radar). If you are unfamiliar with the EM spectrum, you can read a longer description here.

Optical Earth observation, the aim of our course here, focuses on a particular part of the spectrum that includes light visible to humans, and some infrared radiation. At times, we will make reference to additional information that helps to supplement optical images – such as thermal or radar measurements. The main thing to bear in mind is that in this course we are focusing on reflected sunlight in a relatively narrow part of the EM spectrum, where there tends to be most solar energy available and on which almost all the processes of life rely

During the nineteenth century, the development of photography meant accurate images of events and people could be captured for the first time. The beginnings of Earth observation can be seen in photography that was taken out of curiosity – particularly from elevated perspectives, balloons, kites, even carried pigeons, for military intelligence, or for the new and rapidly growing news sources, and even for showing the aftermath of natural disasters.

Within decades of the first photographs, the first aerial images were being produced. The oldest surviving examples were taken in Massachusetts, USA taken by SA King and JW Black in 1860. For example, JW Black’s image of “Boston, as the eagle and wild goose see it”, which was taken from a balloon. The value of being able to see large areas from above was immediately recognised and a photograph from a kite famously revealed the devastation caused by the 1906 San Francisco earthquake. A lightweight camera kit attached to a pigeon was pioneered around the same time, with results being presented by Julius Neubranner at the 1909 Dresden International Photographic Exhibition

Aerial photography had many applications in the military. During the first world war, troop placements were imaged from aircraft. Armies from different countries invested in the development of aerial imaging – but some of these aircraft were repurposed for civilian Earth observation.

All of these early attempts relied on the photographs being returned to the ground, recovered, and examined by human eyes. This was a particular challenge for images taken from space, with elaborate mechanisms being developed for recovering film canisters for the early spy satellites - the Soviet Union’s Zenit system, and the United States’ CORONA programme.

When digital imaging, and even video, began to take over from photography in the 1980s, the main challenge was in having sufficient memory for data, and transfer opportunities and speeds to return data to the ground. The development of weather satellites was a crucial early application of Earth observation from space - tropical cyclones forming over the oceans could now be detected and monitored allowing ships to avoid them, and communities to prepare for landfall.

Optical Earth observation in the 21st century still relies on the same reflected sunlight, but with much more sophisticated systems for data gathering, relay and interpretation, and with a vast number of other instruments offering additional information, augmenting and complementing what the human eye or the camera can see. Optical Earth Observation is still vital to meteorology, as well as offering opportunities to monitor the processes of life. New applications for optical EO are developing because of the recent rapid increase in high-resolution mapping.

The information we acquire from space must be backed up by observations from the ground – this is done in the calibration phases of satellite instruments. Prototypes of instruments are often flown initially on aeroplanes to prove that they detect the signals that are needed, and during the test campaign ground observations will be taken to ensure the measurements are correct. Ground observations, and buoys in the ocean, take measurements to supplement satellite information, and to check that satellites are seeing clearly .

Featured Educators:

  • Dr Mathias Disney

Don’t forget you can download the video, transcript and take any quizzes available with the links on the right.