There are two estimates of the photoemission current from LAP1 sweeps of a sunlit probe.
I_PH0_60M in PH0 files is a statistical estimate from several sweeps (over 60 minute
windows), while I_PH0_S in the ASW files is an estimate from a single sweep with larger
uncertainties but higher time resolution (usually 160 s). As LAP1 has shown no significant
contamination effects, these estimates should be directly proportional to the EUV flux at the
Rosetta position in the 20-130 nm band [Johansson et al, 2017]. For LAP2, the same
techniques have revealed a lower photoemission at the start of the cometary phase of the
emission, and a sharp drop in photoemission after significant thruster firings (e.g. dayside
excursion, 60% decrease) with sporadic recoveries and relapses. We therefore only use LAP1
based values.
While there is no other source of photoemission measurements than LAP, its value is
controlled by solar EUV radiation which is known from e.g. TIMED and SDO at Earth and
MAVEN at Mars. Photoemission values by both methods were presented by Johansson et al.
[2017] and compared to Earth and Mars data. The two methods were found to give consistent
results, also in agreement with a third independent method immune to instrument offsets.
However, around perihelion all methods returned about 50% less photoemission than
expected from the Earth and Mars EUV fluxes. This may be a real effect, for example because
of attenuation of solar EUV radiation by large numbers of small dust grains at large distance
from the nucleus. It is also possible that this somehow relates to probe surface contamination,
though no other such effects have been noted on LAP1.
This is a preliminary data set which will be replaced by another in a few months.
Version:2.4.1
There are two estimates of the photoemission current from LAP1 sweeps of a sunlit probe.
I_PH0_60M in PH0 files is a statistical estimate from several sweeps (over 60 minute
windows), while I_PH0_S in the ASW files is an estimate from a single sweep with larger
uncertainties but higher time resolution (usually 160 s). As LAP1 has shown no significant
contamination effects, these estimates should be directly proportional to the EUV flux at the
Rosetta position in the 20-130 nm band [Johansson et al, 2017]. For LAP2, the same
techniques have revealed a lower photoemission at the start of the cometary phase of the
emission, and a sharp drop in photoemission after significant thruster firings (e.g. dayside
excursion, 60% decrease) with sporadic recoveries and relapses. We therefore only use LAP1
based values.
While there is no other source of photoemission measurements than LAP, its value is
controlled by solar EUV radiation which is known from e.g. TIMED and SDO at Earth and
MAVEN at Mars. Photoemission values by both methods were presented by Johansson et al.
[2017] and compared to Earth and Mars data. The two methods were found to give consistent
results, also in agreement with a third independent method immune to instrument offsets.
However, around perihelion all methods returned about 50% less photoemission than
expected from the Earth and Mars EUV fluxes. This may be a real effect, for example because
of attenuation of solar EUV radiation by large numbers of small dust grains at large distance
from the nucleus. It is also possible that this somehow relates to probe surface contamination,
though no other such effects have been noted on LAP1.
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.
Photosaturation current derived collectively from multiple sweeps
Quality value in the range 0 (worst) to 1 (best).
Corresponds to goodness of fit or how well the model fits the data.
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)