Column Descriptions for the MSI Pre_Eros Observation Guide: The MSI Pre_Eros observation guide describes some basic information about each MSI observation that was acquired during the NEAR mission covering the time period from launch, 1996/051, through the Earth Moon Flyby activities ending on 1998/026. The data contained in this spreadsheet were acquired using a different sequence process than those found in the Eros spreadsheets, hence different types of supporting files are available for each. The organizational structure is different as well. The following fields are recorded: 1. Orbit N/A for this spreadsheet. 2. Sub-solar Latitude - N/A for this spreadsheet. 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. 4. Year-Doy This describes the year and day of year of the start of the observation. 5. Sequence - In this Pre_Eros spreadsheet, this column is a link to the STOL script for the sequence. Sometimes this is preceded by a summary description of the sequence. If this is not availalbe, the pre_eros_seq_archive.txt has some examples which will show you how to interpret the STOL script. Please refer to the observation_overview.txt file for the names and locations of additional files available such as imagelists. 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 (tbd) Up to 12 unique Sequence Definitions were resident in the MSI DPU during the Pre_Eros phases. Each of these Sequence Definitions contains a parameter, the Seq ID, which is an integer between 1 and 12, 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). Seq Defs were executed by calling the Seq ID. We could redefine the parameter values in any or all of the Sequence Definitions at any time during the mission. There is currently no SeqID log available for this period as in the Eros phases. But you can go to the STOL sequence file and find where the SEQ ID has been loaded just prior to the observation. A better way to get the same information is to look in the image header where you will find listed the compression, exposure values, and so forth for that image. An imagelist (if available) is another way to get an overview of some of this information. 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 lists the type of compression used for the images acquired in this observation. (tbd) 13. Description A short description of the observation. 14. Detailed Description - In a few cases there are text files that offer more detailed information. They are linked from the spreadsheet. The observation_overview.txt also contains detailed descriptions of many observations and events. 15. Gifs These are plots which attempt to show the imager field of view plotted against the target body. The only plots available in the pre_eros spreadsheet are for Earth Moon Flyby and for Mathilde. The Earth plots were made in IDL because it was the only available means of showing continent outlines. The Moon and Mathilde plots were made with our visualization program, Orbit. For Mathilde, the large triaxial ellipsoid is not Mathilde, but represents the navigation uncertainty region.