From: "Anne Raugh" To: "Anne Raugh at Fred Net" Subject: Re: Home Sick (fwd) Date: Tuesday, October 18, 2005 11:46 AM ---------- Forwarded message ---------- Date: Mon, 17 Oct 2005 13:03:10 -0400 (EDT) From: Ludmilla Kolokolova To: Anne Raugh Subject: Re: Home Sick > I'm going home sick. I don't think I'll be in tomorrow and after that, I > don't know. I'm bringing home some data work to do, including the DFMI > data. Ifyou can email me the calibration notes and any other documentation > I should include, I'll finish it up and get it in to EN, maybe in time for > the current build. Anne, sorry to hear that you are sick. I hope, you will get well soon. Below I repeat the calibration information that I had got from Tom Economou and sent it to you a couple of weeks ago Please, let me know if you need something else. Ludmilla ============================================================ data/ ----- o In the Acoustic Sensor values, particularly the high & low bumpers, the values around close approach do not seem reasonable - the "cumulative count" increases and decreases a number of times, but there is no documented instrument problem or rollover that might explain this. An explanation is needed. The acoustic sensor counters counted the number of time intervals that the signal from the sensor exceeded a certain threshold. This meant that a large impact would produce a large number of counts and a small one a small number. Since the count rate was generally expected to be very low, the possibility of confusion (i.e. not knowing if the number of counts was due to one, two or more actual impacts) was not expected to be a major problem. The strength of this approach was that an indication of the mass of particles could be obtained even when the peak signal from the sensor saturated the instrument. The disadvantage was the possibility of multiple impacts in a counting period (0.1 to 1 sec depending on PVDF trigger) and the possibility of multiple counter overflow. As the acoustic subsystem was a last minute addition after the data rates had already been fixed, the counters had a full range of only 0 to 255. This explains the steps in the counts. The counters start at zero and increment each time there is an impact. Several times during the encounter (~9), the counters overflow. From the statistical analysis it looks as there are no multiple overflows (i.e. counts greater than 256 within a time interval). o PVCF: Highest mass threshold of small area detector has zero counts. Is this a reasonable result given results on large area detector? Should be PVDF, not PVCF There were no high mass particles detected o Acoustic sensor - not clear whether cumulative counts or count rates. One bumper microphone drops way down - is this a reset? Is it saturation? Is it rollover? See above. o Documents say acoustic time resol = 1 sec and PVCF resol = 0.1 sec. What is the meaning of the millisec resolution in the table? The referee refers to the column that shows the spacecraft time at the moment when the data were recorded. This time has the accuracy of milliseconds (that is the accuracy of the on-board clock). But it can be seen that the data were recorded not more often than 1 per second. o Need good calibration data for impact sensors (density dependence, etc.). Provide guidance on which calibration to use and how much uncertainty there is in the calibration. (paper quoted uncertainty of factor 3!) Use the values from the Table 4 in the paper by Tuzzolino et al. "Dust Flux Monitor Instrument for the Stardust mission to comet WIld2", JGR, v.108,E10,8115, 2003. The main uncertainty in calibration comes form the fact that the calibration was done for soda lime glass and aluminum particles but real particles are of different composition and we do not know how well this calibration reproduces, let say, organic, ice, or carbon particles. Also, the calibration samples were spheres whereas the real particles are irregular. The influence of this also hard to estimate quantitatively. The team is convinced that the slope of the calibration lines is correct but the reference point can be shifted up or down by the way they cannot estimate. document/ --------- o The Small Sensor reported no impacts at the m4 threshold, but there is no mention of this in the documentation. The lack of results should be noted and explained. Just there were no particles detected. dfmical.asc and dfmical.pdf o The times recorded in the data file need some additional documentation. Specifically, we need to know the relationship between the reported time and the point of measurement. Indicated time is the spacecraft time o Provide some additional explanation and guidance on how and when to apply the two different calibration constants. Add a discussion of the uncertainty in the calibration. Use the data from Table 4, Tuzzolino et al. paper, for calibration. See above about uncertainty.