## 2 Historical Data
### Satellite Photography and Multispectral Imaging  
Innovations in films, lenses and aerospace engineering enabled the next generation of surveillance: satellite photography. These sensors next evolved into multispectral imagers, isolating different spectral components of each image to collect data in multiple bands and expanding the knowledge about the surface that was being imaged. The basics of remote sensing are beyond the scope of this \begin{table}
\begin{tabular}{|c c|} \hline
**Year** & **Aerial Photography Type** \\ \hline
1947 & Ronne Antarctic Research Expedition (vertical and oblique) \\ \hline
1956–1957 & FIDASE (vertical 1:27,000) \\
1964–1969 & U.S. Navy TMA Trimetrogon (vertical 1:38,000 and oblique) \\ \hline
1972–1979, 1986, 1989, 1990–2002 & British Royal Navy (vertical 1:12,000; 1:24,000) \\ \hline
1962, 1986, 1989–2005 & BAS (vertical 1:20,000 to 1:30,000), some medium format vertical \\ \hline
1989 & IfAG (vertical 1:70,000) \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of Antarctic Peninsula aerial photography campaigns. FIDASE, Falkland Islands Dependencies Aerial Survey; TMA, Trimetrogon Antarctica; BAS, British Antarctic Survey; IfAG, Expedition Institut für Angewandte Geodasie. article, and for subject-specific technical treatment of remote sensing theory and definitions, readers are directed to available textbooks (e.g., [26, 27]) and appropriate review articles (e.g., [28, 29, 30, 31]). Declassified surveillance imagery has enabled the change record to be pushed back by decades, especially in regions of strategic interest to the United States, including extensive areas in the Arctic, Antarctic and mountain areas, such as the Himalayas (e.g., [32, 33]). Declassified images from the Argon, Corona, Gambit, Hexagon and Lanyard (collectively known as Keyhole) Programs are online, covering dates ranging from 1960 to 1980 and with ground resolutions available under a meter for some images; although there is a small processing charge (currently 30 USD) for the first request to access a high-resolution archived image, subsequent downloads are free to all users ([[http://earthexplorer.usgs.gov/](http://earthexplorer.usgs.gov/)]([http://earthexplorer.usgs.gov/](http://earthexplorer.usgs.gov/))). In addition, a \"fiducial\" (_i.e._, reference) dataset of decllassified meter-scale imagery of polar areas is available with coverage beginning in 1999. Some coverage is at fixed sites in the Antarctic (various sites in the Dry Valleys and Palmer Station; [[http://gfl.usgs.gov/site_info_antarctica.shtml?current=3](http://gfl.usgs.gov/site_info_antarctica.shtml?current=3)]([http://gfl.usgs.gov/site_info_antarctica.shtml?current=3](http://gfl.usgs.gov/site_info_antarctica.shtml?current=3))) and sea ice areas in the Arctic Basin (designated Beaufort, Canadian Arctic, Fram, Siberia, Chukchi and Barrow), while coverage of floating buoys began in 2009 ([[http://gfl.usgs.gov/site_info_arctic_sea.shtml?current=2](http://gfl.usgs.gov/site_info_arctic_sea.shtml?current=2)]([http://gfl.usgs.gov/site_info_arctic_sea.shtml?current=2](http://gfl.usgs.gov/site_info_arctic_sea.shtml?current=2))) [34]. Multispectral imagery has an enormous range of applications in circumpolar and cryospheric environments. There are many different available sensors (see Figure 1), offering a wide range of combinations of spatial resolution, revisit time, radiometric sensitivity, imaging bands, scene size, processed products, coverage area and data archive. It is therefore important to use these variables to choose the optimum sensor for a particular application. Figure 1: Historical, ongoing and future satellite optical and multispectral sensors (with platforms in parentheses) with some or all freely available data. Mission-specific details: the hatched period for ETM+/Landsat 7 indicates the SLC-off period and the gray section of the fiducial dataset indicates when only fixed-site imagery is available; beginning in 2009, images of both fixed sites’ floating buoys are available. VIIRS, Visible Infrared Imaging Radiometer Suite.