Column Descriptions for the MSI Eros Observation Guides: The MSI Eros Observation Guides are spreadsheets tha describe some basic information about each MSI observation that was acquired during the NEAR mission starting with 1998-210. There is one line per observation. An 'observation' is a convenient unit for organizing the data and refers to the process of sequencing. The observations within the Eros guides were developed using the SEQGEN software. This is in contrast to the sequences prior to 1998 which were built by hand using STOL. A different organizational structure for the supporting files was required for each which is why the spreadsheets were divided in this manner. The following fields are recorded: 1. Orbit/Range An entry in this column identifies either when an orbit correction maneuver was performed, or gives the range to center of Eros. By example, when a value reads "325x266" it means that on that day, the spacecraft entered into an elliptical orbit with radii of 325x266 km. When a single number followed by 'km' is given, it simply means that is the approximate range to center of Eros at the start of that observation. More information about spacecraft orbital position and viewing geometry can be found in the eros_orbital_info.txt file. See also the observation_overview.txt file; in chapter 13 there is a table of maneuvers performed during the orbital mission. 2. Sub-solar Latitude - latitude of a point on Eros where a line connecting the sun and Eros center pierces the surface 3. Observation This is a unique descriptive term identifying the name of the observation. This represents a unit of sequencing which acquired a set of images. The data acquired within an observation were generally taken as a discrete event with a common purpose. In the sequence files, (i.e., 00066_final_sasf.txt) a single 'Request' usually corresponds to one observation in this spreadsheet. The names will be similar but not always identical. Occasonally a 'Request' is broken into several 'Observations'. 4. Year-Doy This describes the year and day of year of the start of the observation. 5. Sequence - In the Eros spreadsheets, this column refers to a subdirectory which corresponds to the 'sequencing week' during which that observation was created. Sequences were generated once per week (duration 1 week) during the orbital phase and were identified by this 5 digit integer which essentially tells you the year and doy of the start of that sequence (98306 was the sequence that started on or about doy 306, 1998). In the corresponding subdirectory you will find the gif plots for that weeks observations, the sequence file (98306_final_sasf.txt), the imagelist (98306.imagelist), and the expanded command files (98306.msi and 98306.nis). More information about interpreting these files can be found in eros_seq_archive.txt. By clicking on the week number, you will be taken to the subdirectory for that week. 6. MET Range This is the range of METs for the observation (spacecraft mets for first and last images in the observation). 7. Start UTC This is the UTC of the first image in the observation. 8. End UTC This is the UTC of the last image in the observation. 9. Sequence ID This column lists all SEQ IDs called for execution during the observation. Up to 30 unique Sequence Definitions were resident in the MSI DPU during the Eros mission phases. Each of these 30 Sequence Definitions contains a parameter, the Seq ID, which is an integer between 1 and 30, that uniquely distinquishes it from the other Seq Defs. A Sequence Definition defines the format by which images are acquired (number of images, spacing, compression, exposures, filters, etc). They were executed by calling the Seq ID. Up to 8 images can be taken with any single execution of a Seq Def. We could redefine the parameter values in any or all of the Sequence Definitions at any time during the mission. For the most part, we were able to keep the set of 30 constant for most of the orbital phase but various factors required that some of them be changed periodically. The msi_seqid_log.txt contains a log entry for each Seq ID, sorted by time, every time that Sequence Definition was changed. It also describes the fields within a Sequence Definition. Therefore, to find the definitions that was resident for a specific observation, do the following: 1) note the start time of the observation, 2) note the seq id used for that observation, 3) go to the msi_seqid_log.txt and look under the seq_id in question and find the line entry with a time that is the most recent prior entry to the observation time. That will be the definition resident for that seq id when that observation was executed. Often more than one Seq Def was used within a given observation. For instance, Seq IDs 20 and 19 were often used to take the 3 color 'cleaned' observations. The auto exposures were taken with Sequence 20, and manual zero exposures were taken with Sequence 19 and they were executed within an observation as a pair. An alternative way to know what compression, exposures, filters, etc were used in an observation is to look in the image headers. The imagelist is also a good source to get an overview, but it does not give compression info (i.e., eros/00066/00066.imagelist) 10. Number of Nonzero Images This is the number of images acquired by this observation which had non-zero exposure values. 11. Number of Zero Exp Images This is the number images acquired by this observation which had zero exposure values. 12. Compression This is a shortcut description of the type of compression used for the images acquired in this observation. Generally, during the 2000 data, when it says Table5, it means Table5, ON, FAST. When it ways Lossless, it means NONE, ON, FAST. See SeqIDs for more detail. Compression info is also available in the image header. 13. Description A short description of the observation. 14. Detailed Description - Almost all observations in the Eros data set have been divided into catagories that represent observation type. Text files exist that offer a description of the observation type, and a listing of all observations within that type. These text files are linked from the Detailed Description column. The files are located in the /eros/descript subdirectory. Companion spreadsheets are available in that subdirectory as well for each observation catagory. The observation_overview.txt also contains detailed descriptions of many observations. 15. Predict Plot - These are predict plots generated by our visualization program Orbit. They show the MSI and sometimes NIS fields of view plotted onto a 3-d representation of Eros shape. Often an observation continued over the course of many hours. During that time, the view of Eros from the spacecraft changed dramatically a it spun below us. Orbit was an interactive piece of software that allowed us to click through an observation frame by frame and watch the view to Eros change with each new image taken (like a movie). It is impossible to capture most of the observation designs in a single plot because the view to Eros changes significantly in as little as 10 minutes due to the spin of Eros. Unfortunately, we didn't have the time to always make multiple plots, nor would it have been practical for this archive. So we tried to at least give the flavor of the observation in the simplest manner with a single plot. Only the frame with the purple/red outline is the one which matches the view to the asteroid shown in the plot. The view of Eros in the plot is how Eros looked from the spacecraft when that image was taken. Remember, Eros spins 360 deg in about 5.3 hours. When all of the other frames were taken the view to Eros was different, including different shadowing patterns. You simply can't show all that in a single plot. Instead the visualization software tries to at least show what territory was captured by those frames by sort of pasting them on to the asteroid (see note below). This is not a perfect process. The frames at times will appear very distorted. Also, since shadows move so quickly in and out of different surface areas, some of these other frames may appear to be sitting on dark surface in the view shown, but that surface may actually have been lit when that image was taken. The reverse is also true. Sometimes a frame will be shown sitting on lit surface, but when that frame was taken, that piece of surface may have been dark. Note: You may notice that frames often appear to be hanging in space off the surface of Eros, instead of pasted right onto the shape model. This is because the software was not able to plot frames on the actual shape model surface until the end of the mission. A work-around was to plot the frames on to a triaxial ellipsoid that was slightly larger than Eros. For most observations the images have been pasted onto a triaxial ellipsoid. The image frames therefore often appear smaller than what the actual projection onto the surface really was (images projected onto a surface that is closer in range will capture less territory). Similarly, frame-to-frame overlap will appear to be less than it actually was. This was something we had to live with. I have subsequently remade some of the plots using the revised software. It is obvious which ones have been redone. The ones that plot on the triax ellipsoid appear to be hanging in space off the surface of Eros. The revised ones appear to be pasted onto the shape model. The point is, take these plots with a grain of salt. ***The yellow outlined frame which appears in some plots is the last frame of the observation. And remember, the red outlined frame is the one for which the given view to Eros is accurate. *** Remember that these are PREDICT plots. Throughout most of the mission, the pointing was quite good, but there were a few times when the ephemeris drifted from predict and we didn't have an on-board update. In other words, if the ephemeris actual ephemeris is different from predict, Eros will appear to drift relative to the mosaic. Another way of saying the same thing is that the mosaic will appear to have moved in tact away from Eros. *** Plots do not exist for every observation. Sometimes there are multiple plots for long complicated mosaic sequences. For most plots there is a short description in the comment area on the plot itself which will help explain the observation. *** The colored axes represent the asteroid body fixed system in Eros. The red axis is the +X, prime merdian (0 longitude). The green axis is +Y, which is 90 E long, or 270 W long. The blue axis is the north pole of Eros, it is also the spin pole, +Z, for the right-handed system these axes make up. Direction of spin of Eros is determined by putting right thumb in direction of blue axis, fingers pointing along +X, red axis, then curl fingers (they should curl toward the green axis). The direction in which your fingers curl is the direction that Eros is spinning. The times shown in the middle of the plot usually represent the bounding mets and utcs for the frames DISPLAYED. Note that sometimes not all the frames in the observation are displayed (for instance for looping circular mosaics, only the first iteration is usually shown because if you plot all of the frames for a 5.5 hour observation it is an unintelligible mess). Met ranges for the entire observations are given in the spreadsheet. Have fun!