This file contains description of NIS and MSI observations for the first moon calibration period. MSI MOON 1: --------------------------------------------------------------------------------------------------- The boresight used is same one we used for Earth observations, and the one we used for Mathilde, where the MSI is 15.04 'short' pixels toward +z from x', and 2.99 'long' pixels toward -y from x'. A 'short' pixel = .000095895 ur, a 'long' pixel = .00016182 ur. ____________________ | 1. RADIOMETRY CAL: | ____________________| see plot /pre_eros/earthmoon_flyby/msirad.gif - this plot shows the three stopped imaging positions for this calibrations relative to moon cresent First we put the moon at the center of the MSI fov and perform an autoexposure test (MSI Sequence 20). This is followed by a 7-filter set, 2 exposures per filter (Seq's 8 and 9). We then put the moon near the +y edge of the frame (the edge of the lit crescent should be 35 'fat' pixels from the right edge of the fov) and then we acquire Seq's 8 and 9 again. Then we put the moon near the +z edge of the fov. The edge of the lit crescent once again should have been 35 'fat' pixels from the bottome edge of the fov and acquire Seq's 8 and 9 again. _____________________ | 2. SCATTERED LIGHT: | ____________________| 1) First we position the field of view so that the moon is just outside the +y edge of the fov such that the edge of the lit crescent is 5 'fat' pixels from the edge of the fov (that positions moon nadir 1.426126 deg from the center of the fov). We settle and then acquire the first 7-filter set (Seq 14). Then we begin slewing at .0088367 deg/sec so that the fov moves away from the moon in the -y direction (down, if you orient image with line/sample 1,1 in upper left corner). Equivalently, moon moves away from Eros in the +y direction (up). That's why this was called the "+y scan". In the imagelist, the positions of the moon are called out in degrees from center of field of view in +y direction. Seq 14 is executed again 140 seconds after the beginning of the slew. Sequence 10 is executed every 140 seconds thereafter while slewing for a total of 7 times. At the end of the 7th image of the 7thexecution of Sequence 10, the moon nadir should be approximately 11.5 degrees from the center of the fov in the +y direction (up from field of view center). No gif plot for this one. Here is an ascii drawing: o moon moves in ^ o +y direction rel. | \ to fov | o - moon / ^ +y (s/c) _________o___________ | | | | | | | | | | | | ----------> +z (s/c) | | | | | | --------------------- 2)Then we position the moon just outside the +z edge of the fov such that the edge of the lit crescent is 5 'fat' pixels from the edge of the fov (that positions moon nadir 1.521608 deg from the center of the fov). We settle and then acquire the first 7-filter set (Seq 14). Then we begin slewing at .0087530 deg/sec so that the field of view moves away from the moon in the - z direction. Moon moves away from fov in +z direction. Seq 14 is executed again 140 seconds after the beginning of the slew. Sequence 10 is executed every 140 seconds thereafter while slewing for a total of 7 times. At the end of the 7th image of the 7thexecution of Sequence 10, the moon nadir should be approximately 11.5 degrees from the center of the fov in the +z direction. See plot: pre_eros/earthmoon_flyby/msiscatz.gif - shows fields of view at imaging positions along the +z slew There is an ERROR in this plot. Arrow depicts movement of field of view away from moon, but the LABEL +Z is WRONG! It should say, -Z. 3) Then we position the moon just outside the -y edge of the fov and repeat the above sequence 1) except this time we move the fov away from moon in the +y direction; moon moves away from fov in -y direction. see plot: pre_eros/earthmoon_flyby/msiscaty.gif - shows fields of view at imaging positions along the slew NIS MOON 1: ---------- ____________ | RADIOMETRY | ____________| There are two mosaics in this calibration. The The first is done with narrow aperture selected. The second with the wide aperture. These mosaics are almost identical except length of scans in the wide is slightly longer than the scans in the narrow mosaic. Mirror position 75 is used for both mosaics. There is no mirror stepping in either mosaic. The boresight is slewed in a 7-tiered raster scan relative to the lit moon center for both mosaics. Direction of scanning is reversed in each subsequent scan. In the plot, the center of the lit portion of the moon is the center of the coordinate system and is defined as a half radius in the +z direction from moon nadir. NIS fields of view are shown as they move relative to that center. First the boresight is positioned in the - z,+y quadrant (upper left of moon in the plot). We begin a scan to the right (+z direction). After 8 seconds of 'runup' the the first execution of NIS Sequence 7 begins which acquires eight 18 second 'observations'. Each 18 second observation consists of 10 seconds of integration, two seconds of rest, 4 seconds of darks, and then 2 seconds which is the 'seconds between observations' (needed to open the shutter again). Eight times eighteen is 144 seconds but you have to subract 2 seconds because the eighth 'seconds between observations' doesn't occur. So the data acquisition period is 142 seconds for each slewing scan. The 'seconds between scans' is 48 seconds. We put in 2 seconds of pad for symmetry (for the final 'sbo' that didn't occur) plus 8 seconds for slew rundown of the current slewing scan, plus 30 seconds for the reposition to the start of the next slewing scan, plus another 8 seconds for runup of the next (slewing) scan. When the second, or for that matter, any subsequent execution of the NIS sequence begins we should be 8 seconds into the slewing scan and at the same relative position in z. We tried to make the NIS data acquisition be spatially symmetrical about the center of the lit crescent of the moon. It's not perfect because of the 8 seconds of rest, darks, and delay on the 8th observation of each scan. We should have delayed the start of the sequence another 4 seconds but I forgot to do that. Oh well. The pointing isn't going to be perfect either because I didn't leave enough time for the reposition in y. We actually start the reposition immediately after the 8th observation in each scan (gives us 38 seconds) but it's not quite enough and in the simulation there's a bit of overshoot in y (.05deg). Eventually it gets back to the correct y position for the scan, but it takes about 35 seconds from the start of the scan (that's 35-8=27 seconds into the next data acquisition sequence). Hopefully it won't be a problem (.05 deg is only about 6 percent of .76 deg). I think I'm nit-picking. In both wide and narrow mosaics the same strategy for design is used. Basically when the fov is at the furthest extremeties of the mosaic, we wanted the moon to be outside the fov, and the edge of the fov closest to the moon to be no closer than about .2 degrees (plus some pad for the boresight uncertainty). See the picture if this is description is unclear (as I'm sure it is). To do this we positioned the top (first) scan so that the bottom edge of the NIS fov is .2 deg + 3 'long' MSI pixels from the top edge of the lit crescent at the center of the scan. The bottom scan is positioned so that top edge of the NIS fov is .2 deg + 3 'long' MSI pixels from the bottom edge of the lit crescent. The 3 pixel pad is because the real NIS offset from x' might be same size as the MSI offset. But we don't know yet, so we're adding it to both sides as margin. The other scans (2 through 6) are spaced equally in y between the first and last. The start and ending positions of the data acquisition portions of each scan (in z) were selected so that the edge of the fov closest to lit crescent is .2 deg + 15.04 'short' MSI pixels from the edge of the lit crescent. The real start and end positions of the scan are another 8 seconds worth away from the moon at the constant slew rate. In the 'wide' aperture mosaic the scans have to be a bit longer to satisfy the above margin criteria because the NIS wide fov is .76 deg in the z direction vs .38 for the narrow aperture. So to put the fov at the same position relative to the edge of the crescent you have to lengthen the scans a bit. To simplify commanding we put a special boresight definition in which would make slewing symmetrical about nadir. First, we define the boresight as the currently known center of NIS 75. Since no NIS-to-x' inflight calibration has been performed to date we used the pre-launch numbers (from Murchie and Hawkins Oct 20, 1995 memo, "Locations of Instruments Footprints in the MSI Field of View") which gives the center of NIS 75 to be 18.9 'short' MSI pixels (.10384376 deg) toward the +z axis from x', and 1.5 'long' MSI pixels (.0139074 deg) toward the -y axis from x'. (A 'short' pixel is .000095895 microrad, a 'long' pixel is .00016182 microrad). Then, on top of that, we made the boresight point a half moon radius (.1320815 deg) toward -z so that when the 'boresight' is slewed or pointed relative to nadir, the center of NIS 75 will slew or point relative to the center of the lit portion of the moon. Summing the two, we make the boresight 0.0282377 deg toward -z, and 0.0139074 deg toward -y from x'. Boresight = (.9999999, -.0002427, -0004928). The following is some data about the pointing. The pointing isn't going to be exactly as listed because we used a single DS56 to do all 7 scans for each mosaic. Using the Nadir-Sun coordinate system you really need a separate 3 dimensional vector to describe the rates for each of the 7 scans. That would have required using 7 DS 40s and 7 DS56's for each mosaic. Too many data structures. So we used a single DS40 and a single repeating DS56. The result is that the edges of each scan will be ever so slightly bent toward nadir for those scans which don't pass directly through nadir. For those of you doing the NIS analysis, you should get a plot of the slewing from Gene. The 'error' because of this will hopefully be insignificant. Here's the data as if the scans were commanded using the dozens of data structures. moon diameter (deg)=.528326 moon radius (deg)=.264163 moon half radius (deg)=.1320815 long pix (deg) = .0092716 short pix in (deg) = .0054944 boresight x,y,z = ( .9999998, -.0002427, -.0004928 ) pad z (deg) = .2+15 short pixels = .2824156 pad y (deg) = .2+3 long pixels= .2278148 The following describe positions for NIS 75 center in z and y relative to lit moon center. Narrow mosaic: 1.Start position of boresight in z of data acq. portion of scan = - half moon rad - pad z - half NIS narrow fov (.19) = -.6044972 deg from center of lit crescent 2.End position in z of data acq. portion of scan = + half moon rad + pad z + half NIS narrow fov (.19) = .6044972 deg 3. Length of data acquisition portion of scan = 2xabove = 1.2089944 deg 4. Scan rate in z = length of data acq.portion of scan/144s = .008395794 deg/s 5. "Runup" length = "run down" length = scan rate in z * 8 sec = .06716635 deg 6. Start position of scan (rel. to lit moon center) = start pos of data acq portion of scan - run up = - .6716635 deg 7. End position of scan (rel. to lit moon center) = end pos of data acq portion of scan + run down = .6716635 deg Wide mosaic: 1. Start position of boresight in z of data acq. portion of scan (rel. to lit moon center) = - half moon rad - pad z - half NIS narrow fov (.38) = -.7944972 deg from center of lit crescent 2. End position in z of data acq. portion of scan (rel. to lit moon center) = + half moon rad + pad z + half NIS narrow fov (.38) = 7944972 deg 3. Length of data acquisition portion of scan = 2xabove = 1.5889944 deg 4. Scan rate in z = length of data acq.portion of scan/144s = .0110347 deg/s 5. "Runup" length = "run down" length = scan rate in z * 8 sec = .0882775 deg 6. Start position of scan (rel. to lit moon center) = start pos of data acq portion of scan - run up = - .8827747 deg 7. End position of scan (rel. to lit moon center) = end pos of data acq portion of scan + run down = .8827747 deg Wide and narrow mosaic y positions: y position of scan 1 = .8719778 y position of scan 2 = .5813185 y position of scan 3 = .2906593 y position of scan 4 = 0 y position of scan 5 = -.2906593 y position of scan 6 = -.5813185 y position of scan 7 = -.8719778