caveats added to MAVEN/MAG

Elena.Budnik
1 parent 2453f459
Showing 2 changed files with 34 additions and 9 deletions Show diff stats
NumericalData/AMDA/MAVEN/MAG/mav-mag-all.xml
NumericalData/AMDA/MAVEN/MAG/mav-mag-pds.xml
@@ -5,18 +5,13 @@
       <ResourceID>spase://CDPP/NumericalData/AMDA/MAVEN/MAG/mav-mag-all</ResourceID>
       <ResourceHeader>
          <ResourceName>1 sec</ResourceName>
-         <ReleaseDate>2015-10-12T10:48:29Z</ReleaseDate>
-         <Description> averged over 1 sec                      
-         </Description>
+         <ReleaseDate>2016-12-12T10:48:29Z</ReleaseDate>
+         <Description> averged over 1 sec from high resolution PDS data</Description>
          <Acknowledgement>Principal Investigator : John E.P. Connerney, NASA GODDARD, Greenbelt</Acknowledgement>
          <Contact>        
             <PersonID>spase://CDPP/Person/John.E.P.Connerney</PersonID>
             <Role>PrincipalInvestigator</Role>            
-         </Contact>
-         <Contact>
-            <PersonID>spase://CDPP/Person/Elena.Budnik</PersonID>
-            <Role>TechnicalContact</Role>
-         </Contact>
+         </Contact>   
          <InformationURL>
             <Name>MAG web page, Summary sheet </Name>
             <URL>http://lasp.colorado.edu/home/maven/science/instrument-package/mag/</URL>
@@ -53,7 +53,37 @@
         <Cadence>PT0.031S</Cadence>     
       </TemporalDescription>
       <ObservedRegion>Mars</ObservedRegion>
-      <Caveats>
+      <Caveats>MAG data products are provided in several useful coordinate systems and at the highest time resolution
+available. The MAG observations contain some known artifacts that you may encounter in your use of the
+data that you should be aware of. These are related to several different sources on the spacecraft that have
+been, and continue to be, under investigation. This message is dated April 10, 2015, and it represents
+our current (and evolving) understanding of the status of the spacecraft and its influence on MAG
+data. These include:
+* rapid magnetic field variations of ~6 nT in magnitude (in spacecraft payload coordinate axes y and z)
+associated with infrequent thruster firings (every few days) that are employed in trajectory correction
+maneuvers (TCM). These are relatively easy to identify.
+* variations (in spacecraft payload coordinate axes y and z) of ~1 nT in magnitude associated with solar
+array currents in circuits at the outer edge of the solar arrays, near the magnetometer sensor. MAG
+processing mitigates these signatures where spacecraft engineering telemetry is available at high time
+resolution. The necessary spacecraft engineering data was made available after Jan 9, 2015, following in-
+flight spacecraft testing to isolate the problem. Prior to this time, we use a coarse indication of solar array
+currents to correct the data, and this correction will be out of time step with the actual needed correction
+part of the time. Corrections applied are listed on each record along with the corrected data. These
+variations may appear as step functions, e.g., when the spacecraft enters eclipse, or slow variations as the
+spacecraft attitude with respect to the sun varies. They were identified in the quiet, weak field
+environment of cruise and when illumination on the solar arrays was more intense than experienced in
+cruise.
+* multiple sinewave variations usually of ~0.1 nT in magnitude, that track the frequency of operation of
+the four Reaction Wheel Assemblies (RWAs). The magnitude of these variations has been observed to
+increase substantially when the RWAs are operated at very low frequencies; at such times they may
+appear prominently in spectra of MAG observations.
+* the "static" or slowly-varying spacecraft field has been estimated using spacecraft roll maneuvers that
+are scheduled to occur approximately every 2 months. The MAVEN static sc field specification was NTE
+2 nT. The MAG data processed for December 2014 use an estimate of the spacecraft field obtained from
+the day 353 2014 magroll maneuvers, the only set performed subsequent to deployment of the APP after
+insertion into Mars orbit. We have yet to verify if this sc field estimate remains relatively constant or if it
+varies over the interval between magroll maneuvers. Investigation of the time variability of this part of the
+sc field is expected shortly.
       </Caveats>    
 <Parameter>
    <Name>b_mso</Name>