This is the README file for LAPISEA LAPISEA contains the Dynamics Explorer-2 Shaft Encoder Angle (SEA) data for the LAPI experiment that was included with the LAPI VAX binary data. The LAPI CDF files were generated by converting the VAX binary format stored at the Space Physics Data Facility (SPDF). The VAX binary format was converted from the original Sigma-9 machine that was used to collect and process Dynamics Explorer telemetry. Four sensors are included within the DE-2 LAPI SEA CDF files: Sensor Parameter Unit valid Range 0 Shaft Encoder Angle index 0 to 1024 The shaft encoder angle measures the offset position of LAPI's scan platform with respect to the LAPI instrument. There are 0.00614921 radians per step of the scanner shaft. Additional quantities are generated as follows: Sensor Parameter Unit valid Range 1 Scanner Encoder Angle rad 0 to 2*pi deg 0 to 360 2 Scanner Angle rad -pi to pi deg -180 to 180 5 Scanner Offset Angle deg -180 to 180 The Scanner Encoder Angle is just the Shaft Encoder Angle converted from an Index to a physical value (there are pi radians in 180 deg). The Scanner Angle is the complement in order to shift the rotation direction of the Shaft Encoder Angle into the spacecraft frame. The Scanner Offset Angle was used to test the calculations of the pitch angle to ensure the correct rotation offset was 0 deg after conversion. There was a possibility that the shaft had an associated offset Angle; however, manipulations of this offset proved that the correct offset was 0 deg (The LAPI sensors had view directions in only one half of its observation plane. Offsets other than 0 deg were shown to incorrectly place an off-axis sensor in the wrong pitch angle or precipitation angle in various hemispheres, and it was only through an offset of 0 deg which were shown correct for all conditions). All variables are stored as 4 byte real numbers where -3.4e+38 is used to indicate a fill value. A status byte is included in the CDFs and indicates the status of processing achieved at Goddard Space Flight Center (GSFC). Status Meaning Number of Bits 0 SPDF Status Flag - All 8 Each bit which makes up the status byte was extracted so that each bit could be individually examined. These were labeled starting at bit 0 as follows: Status Meaning Number of Bits 1 SPDF StatusFlag - Bit 7 1 2 SPDF StatusFlag - Bit 6 1 3 SPDF StatusFlag - Bit 5 1 4 SPDF StatusFlag - Bit 4 1 6 SPDF StatusFlag - Bit 3 1 7 SPDF StatusFlag - Bit 2 1 8 SPDF StatusFlag - Bit 1 1 9 SPDF StatusFlag - Bit 0 1 The SPDF status byte defines the processing undergone when converting the original DE LAPI telemetry from its Sigma-9 format to its VAX binary format. The SPDF status byte was meant to describe the values that were encountered when reading the Sigma-9 magnetic tape. Bits 3, 6, and 7 are contained within status 0. Bit 3 indicates that the SPDF encountered a Bad Sensor ID when examining the LAPI sensors, bit 6 when the SPDF Previous LAPI Sensors Differ from the current sensors, and bit 7 when the SPDF detected a Time Gap in telemetry. The remainder of the bits were not defined in the SPDF documentation. These SPDF flags are specific to LAPI sensor data and telemetry. They do not refer to these SEA; however, they are related because the SEA data is contained within the same VAX binary file to coincide with the LAPI data. These processing status bits may give a clue to missing SEA data in the CDF data file. The SEA values are considered instantaneous measurements. They have no accumulation, only data latency between measurements. SEA measurements were taken every 2 sec. All variables are stored as 4 byte real numbers where -3.4e+38 is used to indicate a fill value.