Observation of Lunar Impact Flashes with the SPOSH Camera: System Parameters and Expected Performance R. Luther (1,2), A. Margonis (2), J. Oberst (2,3), F. Sohl (3) and J. Flohrer (3)
(1) Humboldt Universität zu Berlin, Germany, (2) Technische Universität Berlin, Germany, (3) Institute of Planetary
Research, German Aerospace Center (DLR), Berlin, Germany.
surface temperature) and 5778 K (solar surface temperature):
Observations of meteors in the atmosphere of the Earth have a long historic tradition and brought up
knowledge of meteoroid population and streams in near Earth space (amongst others). Only recently
resulting in 19,300 nm infrared radiation and 500 nm
observations of meteoroid impacts on the dark side of
visible light peaks, respectively. Thus, as the SPOSH
the Moon became technically possible. Since the first
camera system is most sensitive to visible light,
confirmed Earth based observation of a lunar impact
Earthshine is the dominant background signal for our
flash in 1999 [e.g. 2] more than 50 impact flashes
have been registered . Meteoroids bombarding the Moon are not slowed down by an atmosphere and
The amount of background radiation recorded by one
impact with high velocities of up to 70 km/s, causing
pixel depends on the background emitting area. The
a light flash of about 10 to 100 ms duration.
area covered by one pixel depends on the
Continuous observations of the dark hemisphere of
instantaneous field of view (IFOV) that can be
the Moon enable the possibility to improve data of
the meteoroid population as well as to determine impact time and location which can be used for
seismic analysis and interior structure determination. Therefore, it is important to study the various system
with dPixel being the size of a pixel (13,6 μm for the
parameters that determine the possibility of a
SPOSH camera) and f is the focal length of the
successful lunar impact flash detection, which we
telescope. Greater focal length and smaller pixel size
have implemented by numeric simulations. In
result in a smaller IFOV, hence, in a smaller surface
particular, we want to evaluate the performance of
area covered by one detection unit and less
the camera head of the SPOSH camera system 
background radiation. In this way, instrumental set-
up influences the limiting magnitude for lunar impact flash detection. However, smaller IFOV results in a
2. Influence of System Parameters
smaller coverage on the lunar surface and therefore in a lower probability of detecting lunar impacts.
In order to determine the limiting magnitude of an observational system we simulate the background
Another important characteristic of the observational
signal seen during the observation. It consists mainly
system is the integration time of the camera
of two types of radiation: lunar thermal radiation and
electronics and CCD. Fastest observations are done
the sunlight reflected from Earth to the Moon and
by systems with frame rates of up to 60 halfframes
back to Earth, called Earthshine. Each type of
per second [e.g. 4]. Slower systems would collect
radiation is emitted with a characteristic intensity in a
more background signal instead of impact flashes
certain wavelength. As CCD chips differ in their
and, thus, suffer from reduced signal-to-noise ratios.
Binning of CCD’s can increase frame rates on cost of
wavelength, we evaluate the amount of background
resolution, but increases also the lunar surface per
electrons by simulating the two main signal spectra
detection unit by the binning factor and thus
as black body radiation. The wavelengths of
compensates the lower integration times (see
maximum intensity can be calculated by Wien’s
displacement law for temperatures of 150 K (lunar
In contrast, changes in telescope aperture have an
effect on the signal-to-noise ratio. A larger aperture directly increases the amount of collected photons
Evaluating all observational system parameters is
per detection unit. The Poisson-distributed noise
important for understanding measurements of lunar
increases by the square root of the increased signal.
impact flashes and background noise. Impact flash
Thus, doubling the diameter will approximately
measurements will shed light on the properties of the
impacting objects for studies of the origin of the meteoroid population and for assessments of
collision hazards. Successful observations rely on
improving the signal-to-noise ratio and balancing of lunar impact probability which depends on the
3. Observational System
system limiting magnitude as well as lunar surface coverage.
We are planning further observations with the SPOSH camera head at the Liebenhof observatory
At the conference, we will present further parameters
near Berlin. Two telescopes from the observatory and
of our observational system and will discuss its
their specifications are shown in Fig. 1. Both allow
complete coverage of the dark hemisphere of the Moon. Although the TEC Refractor has a smaller
aperture, the system could be less sensitive to light reflections due to its conception as refractor and thus
This research has been supported by the Helmholtz
might suffer less from losses in signal-to-noise ratio
Association through the research alliance "Robotic
due to reflections from the bright lunar hemisphere.
Exploration of Extreme Environments".
In contrast, the Baker Ritchey Chrétien has a larger aperture and due to the larger focal length covers less lunar surface per pixel, resulting in reduced
Earthshine background and better signal-to-noise
 Bouley, S. et al. “Power and duration of impact flashes
on the Moon: Implication for the cause of radiation.” Icarus 218 (2012): 115-124.
 Cudnik, B.M. et al. “Ground-based Observations of high velocity Impacts on the Moon’s surface – The Lunar Leonid Phenomena of 1999 and 2001.” Lunar and Planetary Science XXXIII (2002): 1329.
 Oberst, J. Et al. “The Smart Panoramic Optical Sensor Head (SPOSH) – A camera for observations of transient luminous events on planetary night sides.” Planetary and Space Science 59 (2011): 1-9.
 Yanagisawa M., N. Kisaichi. “Lightcurves of 1999 Leonid Impact Flashes on the Moon.” Icarus 159 (2002): 31-38.
Observatory: TEC 140 Apo Refractor (left, 140 mm
aperture, 980 mm focal length, 0,81° field of view)
and Baker Ritchey Chrétien (right, 250 mm aperture,
1268 mm focal length, 0,62° field of view).
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