Time to Use Historical Data?

Last week we noted how Earth Observation can be used for real-time disaster support, this week we are looking at another significant advantage of Earth Observation, namely historical data.

In-situ measurements are great for right now, and some in-situ measurements do offer historical comparisons. But what if you want to look at something, or somewhere that has not been measured before, or you want information before in-situ measurements started at a site? This is where the archive of satellite imagery comes into its own; where you can go back in time and undertake historical measurements, monitoring and research. So how far back can you go?  Earth Observation technically began in the 19th Century; Gaspard-Felix Tournachon took photographs of Paris from his balloon in 1858 and Alfred Nobel, yes the man of the prize, designed a system to take aerial photographs from a rockets in 1896. Sadly, Nobel died four months before his design took the first photographs in April 1897.  Obviously we can’t go quite this far back!

Landsat Image Courtesy of USGS and NASA

Landsat Image Courtesy of USGS and NASA

Developments in satellite technology took place in the mid-20th Century, with the launch of the Explorer VII satellite in 1959 designed to measure the amount of heat reflected by the earth; and in 1960 the TIROS 1 weather satellite was sent up to produce daily cloud formation images. The first real mapping satellite was the Earth Resources Technology Satellite in 1972 – later renamed to Landsat. Over the years a series of Landsat satellites have been launched, the latest being Landsat 8 last year.  Consequently, there is 40 year archive of Landsat imagery available!

However, before you all start planning your forty year historical data requirements you need to find out if the data you want is available. Over the years as technology has developed the variety of sensors in orbit has increased, the frequency of which each place on earth is passed over has improved and there is greater availability of spectral bands and spatial resolution. All of this gives richness of imagery and data available today, that may not have a long historical tail.

Some imagery is freely available, whilst for others you may be required to pay a fee for access.  These fees can range from ten to twenty pounds for a basic image up to many thousands for a single high resolution image.  Interestingly the French Space Agency, CNES, announced last month that they had agreed to offer free access their Spot Optical Earth Observation data archive for images at least five years old.

Earth observation archives offer a huge amount of data and imagery.  To use it you need to know what is available, where to find it, what it costs and crucially how to interpret it to ensure consistency and comparability across the time period you are using.  So how could you, or your company, benefit from this fantastic resource? If you want to discuss your needs, please get in touch.