Moon Reflectivity
Joachim Köppen ... Kiel, Sep 2022

Some brief explanations

This tool shows the reflectivity of the lunar disc as it varies from the centre to the rim, and how this varies with radio frequency. This is done by an image of the Moon and a plot of the radial profile of the relative brightness.

The main beam of a radio telescope with a Gaussian beam shape may be pointed at any position on the lunar disc to measure the fraction of the power picked up from this brightness distribution.

The reflectivity is measured by radar. Because the Moon is a spherical body with a radius of 1738 km, the surface patches at the centre of the disc are closer to us than the areas closer to the rim. Thus the echo from the lunar rim arrives about 11 ms later than the echo from the centre. This gives the return pulse a specific shape, from which the reflective properties of the Moon's surface can be deduced.
These studies were done before about 1970 with large telescopes, including the Arecibo 300m diameter radio telescope. The data used in this tool are from
J.V.Evans (1969) Radar Studies of Planetary Surfaces, Annual Reviews Astronomy Astrophysics, 7, 201

Hit the Enter key after changing the value in one of the input fields, to show the new image.

The data can be shown as a false colour image (the colour bar at right codes the temperature between minimum (black/violet) and maximum values (red)) or as a contour plot (with the user-chosen values).

Please note that the HPBW usually should be larger than the pixel size in the image. Otherwise the program will take a minimum value for the HPBW in order to prevent computational problems. This is indicated by a light yellow background of the textfield.

Frequency [GHz]

antenna HPBW [°]
beam at X, Y [°]

power fraction in beam:

Mouse position: