FPI Time StandardThe time variable in all FPI data products mark the beginning of the data collection interval. Note that for other MMS data products, the time may mark the middle of the data interval. FPI data products after v1.0 include both the time and a "delta +/-" to indicate the time relative to the data interval. That is, for FPI the delta +/- is [10,0] sec for the SITL data product or [0.03, 0] sec for a DES burst product. It is important for users to understand the time conventions of each data product used especially when comparing data sets. |
According to MRD (461-SYS-RQMT-0019L) RMRD_1307 & RMRD_1363: each spacecraft clock will be kept within 500 microsec with respect to GPS time (1 PPS < 500 microsec of GPS time). CIDP to IDPU ICD (10160.17-CIDP_FPI_IDPU_ICD-01) RC@IDPU_0180 allocates 50 microsec for the delay from CIPD receipt of the 1 PPS and its issuance of the triple-pulse time-at-tone (TaT) According to MRD (461-SYS-RQMT-0019L) FPI was granted a waiver (MMS_DW-0233) to exceed the 100 microsec time-tagging requirement.
In General: FPI time tag difference < 670 microsec with respect to GPS time |
Please note that the timing of individual energy and deflection step combinations is NOT directly inferrable from simple linear spacing.
SPEDAS example code to explictly shift FPI moments to "centered-time":
var_dis=['Ni','Ti_para_l2','Ti_perp_l2','vi']
FOR i=0, n_elements(var_dis)-1 DO BEGIN
get_data,var_dis(i),data=d
store_data,var_dis(i),data={x:d.x+0.075d,y:d.y}; shift FPI data to center time
ENDFOR
var_des=['Ne','Te_para_l2','Te_perp_l2','ve']
FOR i=0, n_elements(var_des)-1 DO BEGIN
get_data,var_des(i),data=d
store_data,var_des(i),data={x:d.x+0.015d,y:d.y}; shift FPI data to center time
ENDFOR
OR:
mms_load_fpi, /time_clip, trange=trange,probes=sc_num, datatype='dis-moms', level=fpi_level, data_rate=fpidatarate, versions=versions, /center_measurement
mms_load_fpi, /time_clip, trange=trange,probes=sc_num, datatype='des-moms', level=fpi_level, data_rate=fpidatarate, versions=versions, /center_measurement
Author for this section: Conrad Schiff |