Island Hoppers: December 2022

Acquiring and processing satellite data was quite cumbersome when I started my career as a remote sensing specialist.

We mainly used data from the Landsat satellites, a NASA/USGS Programme which still is operational today and currently is preparing its next generation of satellites with increased spatial and spectral resolution. A scene of the Thematic Mapper (TM), one of the instruments onboard the satellite, was 185 km x 185 km and costed some 3800 US$. Delivery on magnetic tapes took several weeks. Data processing performed on local computers took hours to days, followed by image interpretation done mainly manually by experts these days.

As the instrument operates in the optical domain, the land is obscured by clouds if present. Therefore high revisit times are desired increasing the probability to acquire a cloud-free scene of the area of your interest. This was one of the biggest bottlenecks of the systems these days in particular for applications requiring multiple observations within short time periods and/or for regions prone to cloud coverage. In fact, there are regions where it took months to finally acquire one cloud free scene.

Access to satellite data has come a long way since then. Today, many data from federal funded satellites is available free of charge on the cloud basically a couple of hour after sensing. Data can be downloaded for further processing or can be processed directly on the cloud.

This is mainly thanks to the United States Geological Survey (USGS) who made Landsat data free in 2008, following the US policy that federal funded data is public data and as such can be freely used, reused and redistributed by anyone with no existing local, national or international legal restrictions.

The 'opening' of the Landsat data archive caused a substantially increase and expansion of its usage in various science and application fields. This success, in addition to the promotion of a free and open data policy by the Group on Earth Observations (GEO), an intergovernmental partnership with more than 100 national governments, supported the implementation of similar policies globally including for the European Union's (EU) Copernicus Programme. The space segment of Copernicus, managed by the European Space Agency (ESA) with dedicated satellites - the Sentinels - is today the largest Earth Observation satellite programme worldwide and its data is free and open.

This allows everybody to quickly access and process satellite data either archived data or recently acquired data. It only requires a smartphone with an internet connection. The images below show my 2022 Sailing Destinations processed on my smartphone in about one hour.

You may say now, well, the spatial resolution is much better when zooming in with Google Maps or Google Earth. Yes, you are right but for high zoom levels Google uses commercial high resolution satellite images and aerial photos taken from drones and airplanes which are costly. In general these images are not up to date. In some areas they even date back a couple of years. The satellite data used to generate the images below in fact were acquired at (or around) the time when I was there with T-Fish. Thus, one of the white dots in the ports or at the anchor places in fact is T-Fish when I was there. By the way, I expect that the next generation of federal funded satellites with a free and open data policy will provide much higher spatial resolution, down to the meter scale which currently is reserved for commercially operated systems.