MMIA and MXGS observations from the same TCP may have different time corrections due to choosing the timecorrection from the observation time rather than the TCP cycle. May cause the time correction to differ by up to a couple of microseconds. Issue has been fixed but older data has not been retroactively updated. To mitigate this issue, calculate the time correction from the MXGS observations as (corrected_datetime_level1 - raw_datetime) and use that correction for MMIA as the new corrected_datetime_level1.
MMIA geolocation may be poor if dhpu_position_used flag is True or NULL. Exact cause is unknown but believed to be due to poor interpolation of the CTRS (X, Y, Z) positional data when said data is missing. This error can cause the calculated geolocation to be outside the FOV (Field of View) of MMIA. Error cannot be mitigated and users are advised to disregard geolocations when the dhpu_position_used flag is True or NULL. In nominal operation the accuracy on ground is of the order of 10 km.
There are no BGO energy conversions in TGF observational data. After each detection in the HED Photo-Multiplier Tubes (PMTs) the PMT experience a voltage drop lasting 20 to 50 μs. Subsequent detections in this period are recorded with decreased energies. The effect is strongest after a high energy pulse. Energy conversions must be corrected for this effect for at least 30 μs after initial detection. Please contact ASDC partners at University of Bergen for aid in converting HED Pulse-Height values to actual photon energies.
A TGF trigger may rarely contain more than 2 seconds of data.
Occasionally MMIA cross-triggers causes the MXGS to grab more than approximately 2 seconds of data for a TGF observation. For these TGF observations, no proper timing can be given for the MXGS photons, and the observations should therefore be disregarded.
MMIA triggered observations containing more than 8 frames are split into several observations.
Due to the limit on downlinking the telemetry data from the instrument, the instrument splits the triggered observation into several separate observations, containing a maximum of 8 frames. In order to identify all the triggered observations downlinked, which belong to a single trigger event, the observations are grouped into one trigger group. This can be identified by looking at the group_id of the MMIA triggered observations.
ISS Time Corrections are not consolidated for LOS (Loss of Signal) resulting in poor time corrections for some triggers. This problem should only very rarely cause errors larger than the absolute time accuracy of ASIM but cannot be mitigated or seen directly from the data. ASDC is working on fixing this issue.
Location and time of official TGF lists may differ from Level1 time and location. The TGF list released contains the timestamp of the first photon that is considered a part of the TGF. Therefore, the timestamp in the TGF list is not the same as the timestamp of the observation containing the TGF. Additionally, the location is calculated separately for the TGF list and there is no guarantee that the location of the TGF observation and the location given in the TGF is the same.
MXGS photons are not strictly time ordered in TGF observations. Users should be aware that the photons recorded by the MXGS are not strictly time ordered due to the sampling method employed by the MXGS Data processing Unit. No correction planned.
DHPU latitude and longitude position is incorrect. The positional data received from the DHPU can in some cases be delayed by up to several seconds and should not be used without secondary confirmation.
MXGS spurious triggers when entering TGF Search Mode from High Background Mode. Before Application SW update in March 2019 the MXGS recorded up to 8 consecutive spurious triggers whenever leaving High Background Mode, typically at high geomagnetic latitudes and exiting the South Atlantic Anomaly.
Timestamp may be up to 20 ms wrong Datetimes as recorded by the ASIM DHPU and delivered to the MMIA and MXGS instruments for time stamping observations are up to 20 ms off.
Corrections for this are sought in the use of correlation with ground-based observations (lightning). Implementation due in 2020.
Datetimes not correct in MXGS Background Observations and MXGS Sampled Detector Count Observations Raw Datetimes and Level 1 Corrected Datetimes are not correct for MXGS Background and Sampled Detector Counts Observations for data before 2019-10-05. The datetimes are up to 10 seconds off. To get the correct raw datetimes use the Time of Latest TCP (UTC Year, second and millisecond) and correct for leap seconds. For Level 1 corrected datetime, use observation’s Corrected Datetime minus Raw Datetime plus the calculation of raw datetime above.’ Correction in future re-processing of these observations.
Conversion from DPU Counter to microseconds is not correct The conversion of the DPU counter to microseconds employed in MXGS TGF observations is incorrect. Resulting error up to approximately 10 μs. Correction in future re-processing of these observations.
MMIA event categorization is less reliable without photometer data In the case of triggered events with the ASIM photometers off, ASIM will still try to categorize the event into UV, lightning etc. Based pm camera data. However, the interpretation of the categorization is different. When the photometers are active, events flagged UV correspond to those that has signal in the VUV photometer. When only the CHU are active, events flagged UV correspond to those with a high ratio 337nm/777nm observed in the CHU .
Stale Position Data During some periods in 2020 ISS position data delivered to ASDC were incorrect. The error manifests itself as ISS position remaining constant, typically for a period of 1 minute.
Stale position data appears as a problem in 2020 on Jan 8, 11 and 20 once each day.
From Jan 23, 2020 to Feb 10, 2020 stale position data reoccurs frequently, reappears on Feb 15, 17, 18, 25 (repeatedly) and 27, Mar 3, Apr 16 and 30, Aug 14 and Oct 30.
Most of the periods of stale position data are up to 1 minute long, though a few periods of several minutes are also found.
In the beginning of March, 2021, an update to the ASDC pipeline took into account the problem of stale position data. Interpolation of position data was made between non-stale data points. Some problems remains at the beginning of the stale position data periods, resulting in a small glitch in ISS position.