CALWELL LUNAR OBSERVATORY
CALWELL LUNAR OBSERVATORY
Prof. Steven Morris (see Sky & Telescope, March 1996 page 99) of the Los Angeles Harbor College suggested an observatory experiment to image the lunar surface using a linear polariser in three different modes. The aim was to possibly determine change in polarisation because of chemical differences, or large-scale strain in surface rocks on the lunar surface. This experiment is now concluded, and the images are provided here at the request of co-researcher Professor Steven Morris.
This experiment has been conducted at the Calwell Lunar Observatory during April/May 1997 to take a series of monochrome CCD images using a linear polariser filter first set in a N-S direction, followed by polarised images of the same area with the filter set in an E-W direction and then without a filter.
Each of the three sets of images were assigned the colours red for N-S polarisation, blue for E-W and green for no filter, to form a single colour image. The unpolarised regions of the imaged lunar surface were expected to appear grey, but those areas with slight polarisation to be coloured.
The saturation of each compound image was increased to 81%, and the slight colour difference were expected to become very noticeable. The small scale coloured features could be imaged later at higher magnifications.
Some of the initial images taken on 19 April 1997 are presented below but, the main series of images were conducted at or near full moon on 23 April 1997 to reduce complications due to angle sunlight, repeated for last-quarter on 30 April 1997 and for first quarter on 13 and 14 May 1997.
The imaging was conducted at a magnification of 180 using a Newtonian telescope quartz driven in right ascension and adjusted as required in declination using DC driven geared motor.
The images were first stored on a Video-8 VCR with date and time and then each frame was captured using a MASS Microsystems frame grabber and Macintosh IIci computer with Quickimage 24 software.
The polariser filter and camera arrangement is shown here:
and the telescope/observatory is shown here:
A typical captured image of the Tycho area of the lunar surface seen here at low power and at a magnification of 180 with the linear polariser set in the North-South direction taken near 11h 35m 28s(UT) as shown here:
The test images were not composited or assigned the necessary colours to determine if any small-scale effects on the lunar surface are revealed, but those from full moon, last quarter and first quarter were and are given below.
Three images were taken on 22 April and assigned the colours Red for N-S polarisation, Blue for E-W and Green for no polarisation. They were converted from grayscale to 32 bit colour (16.7 million colours) using Graphic Converter Ver 2.2.2 and composited as added images using National Institute of Health Image Version 1.58, with the resulting image here:
The composited image above revealed a wealth of colour information, but were NOT as expected in that a wide range in colour resulted. This method used was not ideal, as the assignment of colours to each polarised image in Graphic Converter were too saturated and the NIH Image compositing gave very little control over colour addition.
Each image set was saved as RGB files in Adobe Photoshop version 3.0, assigned the RGB individual colours, layered as 50 % opaque overlay images and then merged into new files and colourised with 81 % saturation to bring out required differences.
Another intial set captured four days before full moon on April 19 with the colouration set towards black rather than red, is shown here:
A promising result from this analysis for the two sets of images taken on 1997 April 22 and one set on April 23 all near full moon are shown here:
Another three images were taken on 30 April near last quarter and were also assigned the colours Red for N-S polarisation, Blue for E-W and Green for no polarisation. They have also been processed using the same Photoshop technique.
The last of the images were taken on 13 and 14 May near first quarter and again assigned the colours Red for N-S polarisation, Blue for E-W and Green for no polarisation. They have also been processed using the Photoshop technique.
Where strain is highest the surface features are seen are colourised as red and where there is little or no strain the features are colourless or gray. It is assumed that the redish colour in these false colour images or Polargraphs, indicates strain in the surface lunar material due to N-S polarisation in the reflected light from the surface material, and that the gray coloured areas have low strain. Hence, the red colouration could indicate that minerals are present in those areas.
The areas shown in red could be more closely examined under increased telescopic magnification (X350 and X750 are available) and similar polargraphs prepared. However, the images captured and examined near last and first quarter moon are a little disappointing, probably due to low contrast in the original image sets, which was further reduced in adopting a 50 % opaqueness for each RGB layer to assist alignment of lunar features before Photoshop merging.
Prof. Morris had expected the merged images to be either, gray where there is no polarisation, slightly red or yellow where there is N-S polarisation or blue or cyan with E-W polarisation. A magenta colour difference which was achieved with non-colourised images is unexpected and it is improbable that chemical indentification from NASA's Apollo reports would be available for such lunar polarisation.
Further work may be necessary to ascertain the significance of this consistent but expected red colour change.
Due to the uncertainty of the colouriser analysis reported above, an additional series of images were taken on 1997 May 25. Here the linear polariser filter was fitted to a 400 mm telephoto lens with the CCD camera attached to achieve complete images of the moon. The images were exposed as before, colours assigned and the Photoshop analysis applied without colourising the merged final image as shown here:
This image reveales a reddish tinge in the lower left area of the imaged moon and could indicate a useful result. Comments are awaited from Steven Morris before proceding further with this series. Some dew formed on the exposed linear filter surface, which decreased the clarity of the three captured images used for merging.
The Lunar Prospector should be launched in November this year and it
will be interesting to re-evaluate our results should data become
available from NASA.