WG Aug 23

[Jan Hollan <jhollan@amper....muni.cz>]

Dear Dr Smith,

I belong to the small group of people who are doing research of the
specifically night environment (measuring the amounts of light). Being a
Czech citizen, I would be pleased to use the opportunity to be present at
the WG meeting in Prague on Aub 23.

I am sure I can prepare a good presentation of my research methods,
results and goals for the meeting. My particular abilities concern digital
imaging photometry using ordinary cameras. I'm using some old types, which
can store images in ``raw format'', to get scene luminances (and, using
fish-eye convertor) lens-plane illuminances.

Using common digital cameras for this purpose is not an idea of mine,
several people suggested such an approach and some brought it into a
commercial result. My effort was to develop an open-source software.
I've demonstrated a viability of such an approach. It was a lot of
labour. But now, anybody can do photometry with my software with ordinary
cameras, without being forced to buy a dedicated astronomical CCD camera.

My presentation at the meeting could bear a name

  ``Digital imaging photometry by common cameras -- methods, results and
    perspectives''.

I've measured, among other scenes, lots of sky luminances and profiles in
this way. As they are colour-coded, it's easy to show the results during
the presentation.

There is one minor problem -- I cannot promise I will present my method
and results myself. I've agreed with an preliminary invitation to make a
lecture and a workshop at the first meeting of Arab astronomers devoted to
light pollution, on Aug 20 to 24 in Lebanon. At the moment it's not sure
they will invite me really (i.e., if the scientific committee will approve
my proposals) but if they will, I'll probably go there. In that case some
of my collaborators would read my presentation -- either Pavel Suchan, one
of the Assembly organisers, or Miroslav Bro\v{z}, a young astronomer.

If you would consider adding my contribution to the Aug 23 meeting, here
are some references to my work in English (there are not many, due to
being Czech I write most info in that language):
   http://amper.ped.muni.cz/light/ida/
 is a directory with my 2005 report to IDA,
   http://amper.ped.muni.cz/noc/krnap/2006/
 is a directory with my recent report to the Czech largest Nat. Park. I
will translate the report to English in June or July.

Pierantonio wrote me that you planned to close the programme in Thursday,
meanwhile it is Friday already. I started to write an intro to my lecture
in the morning, but due to other activities it remained rudimentary. I add
it as a Post Scriptum; having more time, I'd surely write something more
informative.

yours sincerely,
 Jan (Jenik) Hollan

--------------------------------------------------------------------------
                                Jan Hollan
              N. Copernicus Observatory and Planetarium in Brno
Kraví hora 2, CZ - 616 00 Brno                        +420 5 41 32 12 87

                                   home:
Lipová 19, 602 00 Brno                                     5 43 23 90 96

               volunteer of the Ecological Institute Veronica
Panská 9, 602 00 Brno, Czechia                  fax:  +420 5 42 21 05 61

e-mail: hollan@ped....cz             http://astro.sci.muni.cz/pub/hollan
--------------------------------------------------------------------------

PS. -- an intro to my possible lecture at WG meeting:

In all our efforts to restore night environment with its natural amounts
of  light, a problem arises: how much light, man-made and natural is
there around and from where it comes? How it was decades ago? How much
does it vary with time and weather? How much do various individual
anti-LP measures help, like adhering to 0 cd/klm limit?

The The First World Atlas of the Artificial Night Sky Brightness
brought an utterly important snapshot of one quantity, zenith luminance
of clear sky. But there exist another relevant quantities concerning
light-at-night, which cannot be inferred from satellite photometry.
Such as angular distributions of light emissions, amounts of unuseful
light from luminaires, amounts of light from lit vertical surfaces and
from lit terrain. Or as imissions to bedroom windows, to gardens  and
parks, to protected nature areas. These imissions have two main sources
of varying harmfulness -- direct light from luminaires poses mostly far
greater problem than dispersed light from the terrain and the sky (as
regards attraction or  detraction of animals, glare preventing people
and animals to see properly, and the damaged appearance of night
landscape).

Knowing the amounts of light from various sources in any situation, or
being able to measure them if needed, is a prerequisite for any
successful dispute with the polluters -- with the lighting industry, various
businesses, municipalities and even some individual citizens. How large
is the relative pollution: the amount of manmade light with respect to
the  amount of light which would be there in natural conditions? Is it
several per cent, one third, one hundred, ten thousand?

Old instruments are hardly able to give us the answer. Common luxmeters
cannot measure natural night levels of light. Just since one year there
is a novel instrument, a simple Sky Quality Meter (see
www.unihedron.com). However, since the start of the third millenium
there  emerged hundreds of types of common digital cameras which can
store raw data. If they are able to  make exposures over 10 s, and if
the exposure times can be set manually, then any night photometry can
be made with them.

I've devoted myself to develop a method of getting radiometric data from
such  common cameras since 2002. In 2003, first results have been
presented (at Ecology of the Night conference). In 2004, a working
software has been published, made available under GNU public license,
and lots of results have been demonstrated in a large report for the
Czech Ministry of environment. In 2005 and 2006, a lot of night scenes
in the Giant Mountains Nat. Park had been imaged and processed, with
the results described in two reports for the Park administration.

The best instrument for environmental night photometry, in my view, is
a digital camera with a fish-eye lens or convertor. I've solved the
tasks of calibrating its spectral sensitivities, vignetting,
AD-convertor nonlinearity, image geometry and luminance output. Using a
set of exposures in 1:16 steps spanning all the camera abilities, any
scene can be fully described photometrically, excluding the direct view
of  the sun (sunlight can be measured indirectly, using a white matt
surface).

Reliable clear sky luminances had been obtained in such a way,
including estimates of the amount of extinction of starlight in zenith.
In overcast conditions, total emissions from local ground sources had
been measured from the luminous flux density of the light patches in
clouds over them. Proportions of direct and indirect light had been
found, luminous intensities of distant lamps measured. In a lecture I
offer, lots of examples will be demonstrated.

The method is still being developed, but anybody can use it right now
already -- of course, an alternative or additional software could be
written (perhaps  a less command-line one) to make nighttime imaging
photometry a widespread method accessible even to laymen. No need to
buy any special instruments -- a digital camera you have maybe should
be enough.

Quite probably, even jpeg-limited cameras can be used for photometry. I
did not devote myself to this task, but others have. I don't think it's
an important method for future imaging, but in some cases it might be  a
possibility to get luminance values from images made long  ago. Of
course, old astronomical photometry data might be employed for  the same
task, as sky luminance is regarded. As it is a lot of labour,   my
suggestion is, to make an easy fish-eye survey at each relevant sites at
first, and only then reprocess the old photometric data from them.

An unsolved task in my software suite is an automated stellar
photometry, resulting in extinction estimates. A similar task had been
solved for Whole Sky Imager instruments, as shown  in the dissertation
of Cristine Ileana Musat. Unfortunately, she omits  any calibrated
radiance or luminance values for the sky (just gives an example
of luminance profile as a function of pixel distance from image
center). Hopefully, lots of images from such cameras can be  processed
to get sky luminance maps as well -- if their native research teams
would consider it worth a while. A much more laborious way of getting
luminance maps had been undertaken by the National Park Service Night
Sky Team (using a large set of images instead of a single  fish-eye
one), and by Fabio Falchi from ISTIL.