| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains global mosaics of the Dawn VIR band centers and
depths of pyroxene absorption bands, located at 0.9 (band I) and
1.9 microns (band II), from the Vesta encounter. The data set was acquired
during the (High Altitude Mapping Orbit (HAMO), Low Altitude Mapping Orbit
(LAMO), and HAMO-2) mapping phases between 2011-09-30 and 2012-07-24 .
VIR Vesta Observations
======================
The following table contains a listing of VIR mosaics at Vesta.
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VIR mosaics
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Target Spectral Product
Coverage Parameter Name
======================================================================
GLOBAL Pyroxene First Absorption Band Center VMT_MOSAIC-BI_CENTER
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GLOBAL Pyroxene First Absorption Band Depth VMT_MOSAIC-BI_DEPTH
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GLOBAL Pyroxene Second Absorption Band Center VMT_MOSAIC-BII_CENTER
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GLOBAL Pyroxene Second Absorption Band Depth VMT_MOSAIC-BII_DEPTH
----------------------------------------------------------------------
Processing
==========
The archived maps contain four spectral parameters relative to the
strong pyroxene bands observed on VIR data of Vesta's surface
[DESANCTISETAL2012]. The mapped spectral parameters are following:
1. Band center at 0.9 micron;
2. Band center at 1.9 micron;
3. Band depth at 0.9 micron;
4. Band depth at 1.9 micron;
The dataset used to retrieve the spectral parameters includes: High
Altitude Mapping Orbit (HAMO), Low Altitude Mapping Orbit (LAMO) and
High Altitude Mapping Orbit 2 (HAMO2) phase of the mission. VIR data
provided in radiance units were converted into reflectance in order to
calculate the spectral parameters (for more details see VIR
calibration document in the /DOCUMENT directory). The photometric
correction applied to these data is described in detail in
[LONGOBARDOETAL2014] but can be briefly described as radiance (R) is the
product of the Akimov disk function (D) and the phase function (F), R = D*F.
Low spatial resolution Approach and Survey data were acquired at relatively
low phase angles and have been corrected with a ''normal'' disk function
D(incidence=0,emission=0,phase=0). High spatial resolution data from the
HAMOs and LAMO were acquired in orbits with higher phase angles and have
corrected with a 30 deg function D(i=30,e=0,p=30). Below the steps to
derive the spectral parameters, as described by supplementary online
material of[DESANCTISETAL2012].
Band centers:
The band centers were computed with the following steps:
1. Smoothing of the spectra. The spectra have been smoothed with a
boxcar average of 3 spectral channels.
2. Evaluation of the continuum and continuum removal. The BI
continuum has been computed as the straight line between 0.7 and
1.2 micron; the BII continuum has been computed as the straight
line between 1.45 and 2.5 micron.
3. Band centers: after the continuum removal, a polynomial fit around
the band minima has been computed. Band center is the wavelength
which corresponds to the minimum of the second order polynomial
fit around the minima of spectra.
Band depth:
Band depths have been calculated by using the definition of
[CLARKETAL1984]:
1-Rc/Rb,
where Rb is the reflectance at the band minimum and Rc is the
reflectance of the continuum at the same wavelength as Rb.
Projection and Coordinate System:
All of the products use the same projection, a simple cylindrical projection
in Claudia double prime coordinates (SPICE refers to this as Vesta
BODY-FIXED ROTATING coordinates). The geometric information were
derived by using the SPICE kernels available at
[http://naif.jpl.nasa.gov]. The DTM selected to calculate the geometric
information has been produced by F. Preusker and is available from the
PDS as DAWN FC2 DERIVED VESTA DTM SPG V1.0. The map projection was
done onto a sphere with the mean radius of 255 km, and refer to east
longitude positive direction and planetocentric latitude.
The maps are centered at latitude 0.0 and longitude 330.0 in the
IAU-compliant Claudia double prime system. This corresponds to 180.0
longitude in the system used in publications by some team members.
See the Vesta Coordinate System document in the document directory for
details of the Vesta coordinate system. The spatial
resolution is constant throughout the image and is 44.5 pixels/degree,
with a map scale of 0.1 km/pixel. Spatially overlapping data are
averaged (simple) after projection.
Data
====
The data are in PDS format image format and are described by attached
PDS labels.
Ancillary Data
==============
No ancillary data are included in this data set.
References
==========
De Sanctis, M.C., J.P. Combe, E. Ammannito, E. Palomba, A.
Longobardo, T.B. McCord, S. Marchi, F. Capaccioni, M.T. Capria, D.W.
Mittlefehldt, C.M. Pieters, J. Sunshine, F. Tosi, F. Zambon,
F. Carraro, S. Fonte, A. Frigeri, G. Magni, C.A. Raymond,
C.T. Russell, and D. Turrini, Detection of Widespread Hydrated Materials
on Vesta by the VIR Imaging Spectrometer on board the Dawn Mission,
Astrophys. J. Lett. 758 L36, doi:10.1088/2041-8205/758/2/L36, 2012.
Clark, R.N., R.H. Brown, P.D. Owensby, and A. Steele,
Saturn's Satellites: Near-Infrared Spectrophotometry (0.65-2.5/~m)
of the Leading and Trailing Sides and Compositional Implications,
Icarus, 58, p265-281, 1984, doi:10.1016/0019-1035(84)90043-5.
Longobardo, A., E. Palomba, F. Capaccioni, M.C. De Sanctis, F. Tosi,
E. Ammannito, S. Schroeder, F. Zambon, C. Raymond, and C. Russell,
Photometric behavior of spectral parameters in Vesta dark and bright
regions as inferred by the Dawn VIR spectrometer, Icarus, 240, p20-35,
2014, doi:10.1016/j.icarus.2014.02.014.
Preusker,F., F. Scholten, K.-D Matz, T.Roatsch, R.Jaumann,
C.A. Raymond, and C.T. Russell,
DAWN FC2 DERIVED VESTA DTM SPG V1.0,
DAWN-A-FC2-5-VESTADTMSPG-V1.0, NASA Planetary Data System, 2016.
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