LuSci campaign at Penyon in March 2008 Preliminary report E.Bustos, A.Tokovinin 1. Instrument, installation, data processing ---------------------------------------------- Lunar Scintillometer (LuSci) is a simple 4-channel photometer designed to study the near-ground turbulence. The complete instrument description is still pending (in fact, this is a prototype in development), the concept is presented in http://www.ctio.noao.edu/~atokovin/profiler/lusci3.pdf The LuSci instrument was installed by EB on Penyon on March 15, 2008. It is located near the mast at a distance of XX m. The instrument is placed on a tripod at an altitude of ~1m above ground (see IMG_8258.JPG). It can point at the Moon coarsely by rotating along the polar axis. There is no control in declination, but the field of view is quite large (+-20degrees), so the variations of the Moon's declinations should not lead to vignetting. As the flux fluctuations caused by the turbulence are quite small, at 1e-4 level, no vignetting is acceptable. Periodically the instrument is offset to measure the sky background. Fast fluctuations of the flux (with 2-ms sampling time) are recorded as binary data in .bin files. Every 10 seconds, the statistical parameters (flux, covariances) are recorded in the text files with .dat extension. So far, the data are processed by the robust method presented in: http://www.ctio.noao.edu/~atokovin/profiler/restoration.pdf The results are the integrals Cn2(z)*R(z)dz, where z is the distance along the line of sight (range), R(z) are the four response functions peaking at 4, 12, 55, and 200m, approximately (see Fig.2-right in the above document). Here the zones defined by R(z) are called "layers". The integrals are given in m^1/3 units. As the sum of all response functions is approximately one, the sum of the integrals can be interpreted in terms of the ground-layer seeing. We plot the cumulative seeing created by the lowest layer, the lowest two layers, etc. Note that the altitudes of the layers depend on the air mass, because the layers are fixed in their distance to the instrument, not in altitude. The restoration method will be improved in the future by fitting the data with a continuous function of altitude Cn2(h). This will permit a better interpretation of the results in terms of "seeing" created in different altitude ranges. The results are given in the text files with .res extension. 2. Results ----------- The list of the dates (UT dates of the end of night) and data summary is given below: 2008-03-15 No data 2008-03-16 Bad pointing, no useful data 2008-03-17 1/2 hour of data, not processed 2008-03-18 Good 2008-03-19 no data 2008-03-20 Good. Edit out "glitches"! 2008-03-21 recovered from the previous night. Good. 2008-03-22 no data 2008-03-23 Good, glitches 2008-03-24 Clouds.. Pointing problem. 2008-03-25 Clouds, pointing. Useful after 6:30 (1.5h)? 2008-03-26 Bad, pointing problem 2008-03-27 no data 2008-03-28 Bad, pointing problem At the beginning of the campaign, the instrument was not set up to point at the Moon (no flux detected). The first useful night of data was March 17/18. The data from March 18.a9 are apparently lost (Edison, are these data appended to the 2008-03-18.dat? If yes, I need the new version of this file). There are no data for March 22 (control fault). On March 18, the flux was varying very smoothly, possibly with tiny transparency fluctuations (see 20080318flux.png). Starting from March 20, we see short (~3min) dips in the flux of all 4 channels, apparently caused by the shadows of the guy wires of the tower because there is a small delay between the dips in different channels (see the wires in IMG_8258.JPG). The data corresponding to these periods (see 20080320flux.png) were deleted manually. The number of dips increased on the following nights (see 20080323flux.png). On March 23 and 24 there were clouds (see 20080324flux.png), these nights are not usable. The flux plot for March 24 also shows a linear trend in the Channel 4, most likely caused by the vignetting (Moon's declination has changed). This problem became worse on the subsequent nights, making the data unusable. In short, we have good data for 4 nights (March 18,20,21,23) and few short (<1h) good periods from other nights, neglected in the following.The plots 20080318.png etc. shows the variation of the ground-layer seeing as measured by LuSci on these nights.