EBZ Dec 25 96 - from e-mail by CNF 21 Jun 96 THEORY OF OPERATIONS -------------------- OVERVIEW OF MDI The Structure Program The scientific objectives related to determining the solar internal STRUCTURE require continuous or nearly continuous observations for many months to years, so this data must be transmitted in the low bandwidth channel. Dynamics Programs The detailed study of the solar convection zone DYNAMICS requires all observable modes for a long interval. During high-bandwidth telemetry intervals exceeding 72 hours, MDI transmits full disk Dopplergrams each minute for the primary dynamics program. For most of the time during a dynamics period the DEP is executing a FRAMELIST* titled PRIME60. This is a set 20 pictures (FILTERGRAMS), two 8 picture (4 up and 4 down) scans of the line plus 4 continuum pictures. What is sent down in the high rate telemetry from this is a VELOCITY (DOPPLERGRAMS) image and either a CONTINUUM image or a LINE DEPTH image. The line depth gives a measure of the intensity of the line and is a measure of the strength of the magnetic field. All of these images are computed by the IP based on the 20 pictures. (The choice between the continuum and a line depth is made by setting a DEP flag. Currently (6/6/96) line depths images are being sent down) The dynamics program can be interrupted in one of two ways. The first is the ALT SEQ (Alternative Sequence, a better name would be alternative framelist.) The second is from a CAMPAIGN FLAG. The alt seq is an alternative pair of framelist that takes MAGNETIC FIELD (MAGNETOGRAMS) for 30 seconds each minute and takes velocity images for the other 30 seconds. Magnetic field images are made by taking pictures with different polarizations. A register in the DEP controls the cadence of the Alt Seq. Campaigns are started via a ground command. This can be done with a TSTOL (A command sent by the S/C Operators) or with NRT commands (Near Real Time, commanding from the MDI/EOF workstation). During the dynamics period campaigns are used if it is necessary to get dumps of on board data (such as to check if the FLAT FIELD** is still good) or to perform tests that are necessary to check the health of the instrument (such as checking focus or for contamination "ice" buildup). Data from the campaigns are sent down in the high rate channel. When either a campaign or the alt seq is being performed it will use 30 seconds of the 60 second sequence. During the other 30 seconds the frame list being executed is PRIME30. Prime30 is basically the same as prime60 except that it is done in 30 seconds and only 1 sweep up and down of the line instead of 2. (10 pictures instead of 20). A series of data products is made from this data and the data is sent down in the LOW RATE (5KB) channel. The data from this channel is used for the long term structure program. During the periods of the year when we are not in continuous high rate mode MDI has two basic modes. Structure and campaign. During periods of structure the prime60 frame list is executed and the data products are sent down the low rate channel. During periods of campaigns we again have high rate telemetry and various campaigns are performed to take advantage of this. During these campaigns MDI will perform special scientific tasks and offers an opportunity to make coordinated observations with other SoHO experiments and with observatories. The beginning of the campaigns can also be used to perform special tasks like data dumps and tests to check on the health of the instrument as was done in the dynamics periods. As with the dynamic periods, during the campaigns, the other half each minute will be used to perform prime30 and continue the structure program. There are a few special campaigns that completely displace the structure program. Because of the architecture of the DEP software, there must a prime half, so the prime that goes with such campaigns is called PRIME00. It takes essentially 0 time. * FRAME LIST A frame is a set of instructions in the DEP that set the mechanisms positions, the exposure time, and tells the camera what messages to send to the IP. A frame list is a list of these frames. ** FLAT FIELD A pixel by pixel map used by the on-board processor to adjust for inherent inconstancies in the image. The on-board flat field is used for those images that are sent down in the low rate data and are based on continuum images. For the velocity based images, flat fielding is not necessary since the images are based on differences between pictures. TYPES OF COMMANDS - NRT (Near Real Time) - Commands sent from the experimenters workstation that are transmited through the chain of computers to the S/C without intervention. - BKG (Background) - Commands ftp'ed from the experminters workstation to the EOF and than transmitted through the chain to the S/C. This type of commanding is used for large loads such as the MDI Flat Field to try to miminize the interference with the other experiments. - Delayed - Sent by the FOT at a given time or within a given time period. These commands are used when commands need to be sent at a certain time but NRT or experiment operators will not be available at that time. - TSTOL - Commands sent by the FOT in a procedure. These are used when it is necessary to send commands to MDI but NRT is not available or practical. The procedures that switch MDI to and from high rate mode are performed in TSTOLS. TYPES OF IMAGES - Velocity (dopplergrams) - Line Intensity - Continuum Intensity - Magnetic Field (magnetograms) TELEMETRY MODES - VC0 - low rate housekeeping - VC1 - low rate science - VC2 - high rate data mode (Data goes to JPL and EOF) - VC3 - high rate data mode (Data goes to JPL and is later sent to Stanford) - VC4 - high rate data dump TREE OF OPERATIONS - Computers: IWS -> ECS -> CMS -> POCC -> DSN -> Spacecraft - People: IWS -> SOC -> FOT