two LAP probes could be used to measure the component of the electric field along their
separation vector, by measuring the voltage of them, taking the difference and dividing by the
separation distance (5.0 m). Each probe could be fed by a bias current as is typically done on
electric field instruments in tenuous plasmas, or be disconnected from the bias circuitry to
ensure a good zero bias current (floating probes) as is typically done on sounding rockets.
Bias currents were used in the early part of the mission, but when the comet ionosphere
developed, the floating mode was found to give much more consistent data. Only data from
the floating mode have been used for providing E-field data, and only when both probes are
sunlit.
Positive value refers to electric field pointing in the direction from probe 1 to probe 2.
The booms are not equal in length (2.24 and 1.62 m) and mounted on a big spacecraft (solar
panel wingspan 32 m), so one cannot expect LAP to provide a useful DC electric field estimate.
A moving average of the E-field over 32 s is therefore subtracted from the data in the EFL files.
The effective bandwidth of the data therefore is about 0.03 Hz to 20 Hz, the upper
limit set by the analog anti-aliasing filters. Note that the filtering may distort the lowest
frequencies.
There are no external comparison data for assessing the absolute accuracy of the LAP E-field
measurements. The data themselves look very clean and well behaved [Karlsson et al., 2017;
André et al, 2017], with very little of common mode signal remaining, despite the s/c poten tial
being both high and highly variable. The technique with floating probes is proven on numerous
sounding rockets in the terrestrial ionosphere [Maynard, 1998].
This is a preliminary data set which will be replaced by another in a few months.
Version:2.4.1
two LAP probes could be used to measure the component of the electric field along their
separation vector, by measuring the voltage of them, taking the difference and dividing by the
separation distance (5.0 m). Each probe could be fed by a bias current as is typically done on
electric field instruments in tenuous plasmas, or be disconnected from the bias circuitry to
ensure a good zero bias current (floating probes) as is typically done on sounding rockets.
Bias currents were used in the early part of the mission, but when the comet ionosphere
developed, the floating mode was found to give much more consistent data. Only data from
the floating mode have been used for providing E-field data, and only when both probes are
sunlit.
Positive value refers to electric field pointing in the direction from probe 1 to probe 2.
The booms are not equal in length (2.24 and 1.62 m) and mounted on a big spacecraft (solar
panel wingspan 32 m), so one cannot expect LAP to provide a useful DC electric field estimate.
A moving average of the E-field over 32 s is therefore subtracted from the data in the EFL files.
The effective bandwidth of the data therefore is about 0.03 Hz to 20 Hz, the upper
limit set by the analog anti-aliasing filters. Note that the filtering may distort the lowest
frequencies.
There are no external comparison data for assessing the absolute accuracy of the LAP E-field
measurements. The data themselves look very clean and well behaved [Karlsson et al., 2017;
André et al, 2017], with very little of common mode signal remaining, despite the s/c poten tial
being both high and highly variable. The technique with floating probes is proven on numerous
sounding rockets in the terrestrial ionosphere [Maynard, 1998].
This is a preliminary data set which will be replaced by another in a few months.
| Role | Person | StartDate | StopDate | Note | |
|---|---|---|---|---|---|
| 1. | PrincipalInvestigator | spase://CNES/Person/CDPP-AMDA/Anders.Eriksson | |||
| 2. | DataProducer | spase://CNES/Person/CDPP-AMDA/Erik.Johansson |
Web Service to this product using the HAPI interface.
Access to Data via CDPP/AMDA Web application.
Electric field component, calculated on ground by
taking the difference between floating probe measurements on both probes and
dividing by distance, (V_P2-V_P1)/L. Positive value refers to electric field
pointing in the direction from probe 1 to probe 2.
Number that describes the exact combination of onboard s/w averaging and downsampling. The exact values are pointers into a table
that describes both the number of samples that are averaged over and the downsampling rate
Quality flag constructed as the sum of multiple terms, depending on what quality related effects are present. Each digit is either in
the range 0 (best) to 7 (worst), or 9 (not used).