Russian Aviation and Space Agency Institute for Space Research NASA 2001 Mars Odyssey page 1 Workshop Workshop HEND HEND - - 2002 2002 Procedures of HEND data Procedures of HEND data convolution for mapping of convolution for mapping of neutron Martian emission neutron Martian emission Workshop Workshop “The First year of HEND operations on the NASA Odyssey “The First year of HEND operations on the NASA Odyssey Mars Mars Orbiter” Orbiter” Moscow, Russia May 20-22, 2002
Transcript
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 1
Workshop Workshop HENDHEND -- 20022002
Procedures of HEND data Procedures of HEND data convolution for mapping of neutron convolution for mapping of neutron
Martian emissionMartian emission
WorkshopWorkshop“The First year of HEND operations on the NASA Odyssey Mars “The First year of HEND operations on the NASA Odyssey Mars
Orbiter”Orbiter”
Moscow, RussiaMay 20-22, 2002
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 2
Workshop Workshop HENDHEND -- 20022002
The signal detected by HEND consists of:
• Flux of neutrons from Mars (this we need to know to build maps of Martian neutron flux)
• Flux of secondary neutrons generated in Odyssey by isotropic galactic cosmic rays (this we know and subtract from detected signal to determine 1)
• Flux of secondary neutrons generated in Odyssey by radiation from Mars (this we need to know, but at present stage this isn’t determined value)
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 3
Workshop Workshop HENDHEND -- 20022002
The flux of secondary neutrons generated in Odyssey by isotropic galactic cosmic rays is determined during aerobraking phase of mission.
This value was defined as signal obtained at big (> 104 km) distances from Mars.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 4
Workshop Workshop HENDHEND -- 20022002
4
cos124 Marsiii BNC
where Ni – measured counts during i-th frame,
Bi – counts of isotropic galactic cosmic rays in i-th frame,
Mars – angular radius of Mars as seen from Odyssey
Ci – signal from Mars in i-th frame.
The HEND have time resolution is 19.2 sec. During this interval instrument accumulate counts for all detectors, and only after end of interval measured counts are write in spacecraft memory and transmitted on Earth. This interval is called frame.
Accordingly, the signal from Mars in i -th frame we define as:
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 5
Workshop Workshop HENDHEND -- 20022002
Due to HEND placed on spacecraft with very complex shape, some constructive elements and instruments are between HEND and Mars.
Here shown a projection of HEND’s field of view, geometrical visible part of Mars (orange area), spacecraft
At present stage this effect not takes in to account. But in future analyses it must be done.
shadow (violet area) and area limited by physical neutron collimation in soil and atmosphere (blue area). The Martian neutrons only from blue area can be detected by HEND.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 6
Workshop Workshop HENDHEND -- 20022002
Building the Map
1. On the surface of planet we make a mesh with selected size of pixels. In each pixel we will independently accumulate counts and exposure time.
2. We select a time interval, detector and set of channels to create map.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 7
Workshop Workshop HENDHEND -- 20022002
3. To minimize computing time we assume the trajectory projection during i-th time bin is well fitted by line.
4. Moving through selected time interval we going from one frame to another. For each frame we determine the fractions ( k1, k2, …, kn ) of the trajectory projection on Martian surface length corresponded this pixel:
L
lk ii
where li - length of a part of trajectory projection which lay in i -th pixel,
L – total length of trajectory projection for current frame.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 8
Workshop Workshop HENDHEND -- 20022002
According this fractions ki for selected frames we accumulate counts and exposure time in all pixels on map:
exposurei
ii
n
jijj
exposurei
n
jijji T
EFktTkCE
00
where Cj – count in j-th frame,
tj – duration of j-th frame,
kij – fraction of j-th frame length in i-th pixel,
n – number of frames in selected time interval,
Ei – total counts accumulated in i-th pixel,
Tiexposure – total exposure time for i-th pixel,
Fi – average flux in i-th pixel.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 9
Workshop Workshop HENDHEND -- 20022002
The map of fluxes is produces by ratio Fi . This ratio is well determined, if Tiexposure enough large (for example, Tiexposure > 60
sec).
The maps for exposure time accumulated during Mapping stage of the Mission from February 18 to May 16 (~320 000 frames).
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 10
Workshop Workshop HENDHEND -- 20022002
Due to orbit of the 2001 Mars Odyssey have inclination ~86° where are two areas around North and South poles with ~250 km radii which spacecraft don’t cross. Therefore, using this maps building procedure we will never fill polar pixels of map if theirs size < 4°.
So, in future we need to develop new procedure, based on “reverse scattering” of measured counts on visible from spacecraft Martian surface.
Russian Aviation and Space AgencyInstitute for Space Research
NASA 2001 Mars Odyssey page 11
Workshop Workshop HENDHEND -- 20022002
Russian Aviation and Space AgencyInstitute for Space Research
