The 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.
SPEDAS Notes for FPI Time Tagging
SPEDAS code to 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