Outer planets ablaze at 1.5 microns

Astronomer Mike Brown at Caltech hunts in the outer reaches of the solar system. He usually concentrates on what is called the Kuiper Belt which extends from the orbit of Neptune out to about twice as far as Neptune's orbit. He recently used the Keck telescope in Hawaii with the intention of imaging Neptune's moon Triton, but the views of the planet itself, and closer neighbour Uranus, were too interesting to ignore. The Keck's adaptive optics system, which compensates for turbulence in the earth's atmosphere, produces stunning results.

Neptune, glowing like a demonic cricket ball, shows the two distinct bands which are glowing at the imaging wavelength of 1.5 microns (1500 nm). Of course these are not really 'hot' since the surface of Neptune is -200 C and the bright bands will only be a few degrees warmer. These correspond to faint but visible features on Neptune's 'surface'.

With Uranus the main features are the rings, which stand out distinctly given the low level of radiation from the planet itself, and the spot to the top left which is the moon Miranda. The bright spots on the surface are clouds. This is notable because the 'surface' of Uranus, in visible light, is almost devoid of any features (although, as the 'northern' uranian hemisphere warms up some banding is appearing).

There is more at space.com.

RW Wood took infrared photographs of gas giants Jupiter and Saturn at the end of October 1915. He had been granted use of the 60 inch reflector at Mount Wilson and took photographs through infrared, yellow, violet and ultraviolet filters. His infrared filter had a band-pass of 700 nm, with its upper limit being determined by the plate sensitivity, which was probably less than 800 nm. In this case infrared photographs showed fewer features than visible light whereas belts were clearly shown on the violet and ultraviolet plates. (It is not possible to record a wavelength as long as 1.5 microns using photographic emulsion, so an electronic sensor has to be used, although this is not thermal imaging. However, this wavelength is still within an atmospheric window for infrared.)

You can read Wood's 1916 paper on the SAO/NASA Astrophysics Data System (ADS). It is entitled Monochromatic Photography of Jupiter and Saturn.

[My thanks to Mike Brown for permission to reproduce his images here.]

Infrared invisibility cloak

RV Jones, in his excellent book on British scientific intelligence during the Second World War, called Most Secret War, tells the story of a German attempt to camouflage submarines so that they blended into the sea at both visible and far-infrared/thermal wavelengths. They developed a painting scheme which combined a black undercoat with a top layer of varnish that included powdered glass in suspension. To the naked eye the boat would look grey, presumably like the grey north Atlantic, but to an infrared viewer it would look dark, again like the sea. The properties of the undercoat, glass and varnish were such that infrared passed straight through and was absorbed by the undercoat while visible light was refracted by the glass and gave a grey appearance.

This was a neat trick, of which Jones was most complimentary in his book. Unfortunately the British were actually detecting submarines by using radar and not infrared.

This story comes to mind when seeing the news stories circulating about a thermal invisibility cloak called ADAPTIV produced by BAE systems (their press release). The plan is to enable a military object, such as a tank, to either blend into the background or to appear to be something innocuous. This is done by covering an appropriate surface or two with ingenious hexagonal panels that can be electronically set to give off suitable far-infrared radiation on demand. The trick being the ability to change temperature very rapidly and to adopt a temperature that can be lower as well as higher than ambient.

A thermal imaging camera can be used to pickup what is behind the object and use the ADAPTIV panels to show this on the opposite surface, thus rendering the object invisible. By replacing some of the output pixels with a different thermal pattern the object can be made to appear smaller and different. It's unclear whether such as system could yet be used by an individual soldier but objects larger than vehicles ... even buildings ... can be cloaked using this technology.

The promotional video [now no longer online] is rather fun, not only because of the 'so natural that you want to go to war' music but also for the shots of ADAPTIV in action. I particularly like how the panels can be used to display advertisements!

Infrared Polaroid

A box of Polaroid Land Infrared Film turned up on eBay a few months ago. I wasn't aware that such a thing existed but there it was, and the seller kindly included photographs of the packaging and the data sheet.

The film was reportedly available between 1964 and 1969 (the data sheet shown was dated May 1967) and was designated Type 413. It was a black and white film sensitive between UV and just beyond 900 nm with a peak at 830 and a trough at 510. Equivalent ASA rating was 200 with a Wratten #87 rising to 600 with a red filter and 800 with no filter.

If anyone knows of any examples taken with this film please let me know.

Simon Marsen's Vampires

You are probably aware of Simon Marsden's atmospheric infrared photographs of ruins and other settings with a supernatural ambience. He uses Kodak HIE infrared film, with its characteristic grain and halation, and usually photographs with strong back-light to increase the day-for-night effect.

Simon has just circulated an email about his next book, due to be published in the UK and USA in October, entitled Vampires: The Twilight World and published by Palazzo Editions. I have to say the cover is stunning, and Whitby Abbey is one of those places of which I've always wanted to take an infrared photograph.

Signed copies will be available (signed by Simon I should add ... in case you've been watching too much Twilight) from Simon Marsden’s website from 1st October 2011: www.simonmarsden.co.uk.

Soviet infrared photography

There is one gap the history of infrared photography of which I have been very conscious: the old Soviet Union. The soviets obviously had infrared film, the movie Soy Cuba made in the early 1960s made extensive use of it, and I found a NASA reference to some colour infrared film being flown on the space station.

Of course, my not reading Russian doesn't help but I have managed to track down an intriguing publication from the American military which is available to buy from the National Technical Information Service. It's a translation of a book by I B Levitin published in 1961, translated in 1967, and titled Photography by Infrared Light (approximately).

The document is described, rather oddly, as a machine translation, which has then been 'tidied up' by a human. Actually it reads quite well. The term used for the film is infrachromatic, though I don't know whether that is a literal translation: but it's a nice term.

According to the book, at that point there were three film types regularly manufactured in the USSR - Infrachrom 760, Infrachrom 840 and Infrachrom 880 - with a 720 version manufactured 'irregularly'. These were made in sheets, 35mm and 'wide film' of 19 and 33 cm width. I did a double-take over that: 33 cm is over a foot! The author notes that the number usually refers to the point of maximum sensitivity.

Agfa in East Germany also made infrared film. Eleven different types are listed, divided into khart (less sensitive more contrast) and rapid (more sensitive less contrast). [The translator notes these names are transliterated from Russian rather than being the German terms.]

The book then goes on to list foreign film types, and this list contains more types than I was aware of so I will list the manufacturers here (as shown in the document):

• Eastman Kodak (USA)
• Ferrania (Italy)
• Gevaert (Belgium)
• Guilminot (France)
• Kodak (Great Britain)
• Kodak-Pate (France)
• Konishiroku (Japan)

Pate is presumably Pathé and Konishiroku Honten was the name for Konica until 1987 (see Wikipedia entry). So the Konica film was older than I realised, by a long way, and it seems Kodak in the UK made film separately from the USA at the time. Of course by the end of its life Kodak's HIE film was only made in Rochester.

Levitin's book is very technical and delves even deeper into the physics and chemistry than Clark. It perhaps deserves a wider distribution but for the moment, if you're interested, you can buy it from NTIS as document number AD663365. NTIS is worth a search anyway, for example it tells us that astronaut Gordon Cooper took infrared photos from orbit on May 16, 1963 during Mercury Spaceflight MA-9 (Faith 7). Of course, now I know about this, a Google search yields several results, explaining that his infrared shots were for meteorological purposes. What I don't know is whether these were the first infrared photographs from space ... I'll have to find out.