| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains global color maps, image cubes, and
absorption band maps created from calibrated data taken during
the PLUTO mission phase by the Linear Etalon Imaging Spectral
Array (LEISA) instrument and the Multispectral Visible Imaging
Camera (MVIC) instrument on the New Horizons spacecraft.
Image cubes are provided per instrument and target body,
covering the surfaces of Pluto, Charon, Nix, Hydra, and Kerberos.
Color maps and absorption band maps for N2, CO,
CH4, and H2O are provided for both Pluto and Charon.
Version
=======
This is VERSION 1.0 of this data set.
Instrument Description
======================
MVIC has 4 filters with identifiers and wavelengths listed here:
name identifier wavelengths(nm)
---------------------------------
BLUE mc1 400 - 550
RED mc0 540 - 700
NIR mc2 780 - 975
CH4 mc3 860 - 910
---------------------------------
Each filter is affixed to a separate CCD array with dimensions
[5024,32]. The instrument is operated by sweeping all four arrays across
the field of view together, with scan motion being perpendicular to the
long axis of the arrays. The CCDs are read out during the scan at a
rate matched to the scan motion so as to operate in time delay
integration mode. Much more information on the instrument is published
in [REUTERETAL2008] and in the instrument catalog file in this dataset.
Level 2 MVIC color data consist of separate frames for each of the four
filters, with units of DN. Header keywords are provided to enable users
to convert to flux units according to procedures described in
[HOWETTETAL2017].
LEISA operates at infrared wavelengths, and its etalon (a wedged filter
with a narrow spectral bandpass that varies linearly in one dimension)
is bonded to the illuminated side of the IR detector. As a result, each
row of detector pixels receives only light of a particular wavelength.
Spectral maps are produced by sweeping the FOV of the instrument across
a scene, sequentially sampling each point in the scene at each
wavelength.
The LEISA filter comprises two bonded segments. The first is a high
spectral resolution segment with Wavelength/dWavelength = 560 covering
a wavelength range from 2100 to 2250 nm, The second is a low spectral
resolution segment with Wavelength/dWavelength = 240 covering a
wavelength range from 1250 to 2500 nm.
Though overlapping spectrally, the filter segments are separate and
adjacent spatially. Plots of wavelength and delta-Wavelength per pixel
row across the complete filter show discontinuities at the bond joint
between the segments.
See the instrument catalog file, [REUTERETAL2008], and the SOC to
Instrument Interface Control Document (ICD) for more information.
Processing
==========
/mosaic: Pluto and Charon Global Color Maps
-------------------------------------------
Mosaics are composed of all MVIC color scans between MET
(Mission Elapsed Time) 0298652198 and 0299178098 for
Pluto and MET 0298891588 and 0299176438 for Charon.
Each scan was photometrically converted to normal albedo by
means of a photometric model [MCEWEN1991] with parameter L=0.65
applied for both Pluto and Charon.
All scans were geometrically registered to the Long-Range
Reconnaissance Imager (LORRI) base map, and then mosaiced into
a single map.
Cylindrical Global Color Map Observations
-----------------------------------------
Color images were taken with the MVIC instrument, which is part
of the Ralph instrument [REUTERETAL2008] on the New Horizons
spacecraft. MVIC is equipped with 6 Time-Delay Integration (TDI)
CCDs (Charge-Coupled Device),
four of which are used for color observations. The other
two are redundant panchromatic TDI CCDs (400-975nm). During
observations, data are recorded from all 4 color TDI arrays
simultaneously [OLKINETAL2017], with bands centered at 895,
870, 625, and 475 nm [SCHENKETAL2017] [SCHENKETAL2018].
For Pluto, the best mapping and stereo imaging scans were at
pixel scales of ~0.65 km/pixel at phase angles of ~38 degrees.
Pluto approach imaging had coarser resolutions at 15 deg phase
angles. The phase angle remained essentially constant at ~15
degrees until the final hours of the Pluto encounter,
facilitating production of a global map with generally uniform
illumination quality.
For Charon, the best mapping and stereo imaging covered the
illuminated Pluto-facing hemisphere of Charon. Due to the high
encounter velocity (~15 km/s) and the slow rotation of the two
bodies (6.4 days), mapping resolution with longitude varied from
~35 to 0.15 km/pixel, while terrains south of about -38 degrees
were in darkness due to polar obliquity at the time of encounter.
Cylindrical Global Color Map Data Processing
--------------------------------------------
To produce photometrically uniform maps of the normal reflectance
of the surface, wherein the brightness of different regions can
be compared at least in a relative sense, a simplified photometric
correction is applied to each image or mosaic to correct for
emission and incidence angle variations across the surface before
they are assembled into the global map.
We used the combined lunar-Lambertian photometric function,
formulated by [MCEWEN1991] and encoded in ISIS3 software (Integrated
Software for Imagers and Spectrometers) [SIDESETAL2017], wherein
the relative degree of lunar and Lambertian photometric qualities,
L, is a function of phase angle. This empirical function is used
to produce maps of the effective bidirectional reflectance of the
surface of Pluto and Charon, normalized to common viewing
conditions across the surface, in this case, the approach phase
angle of 15 deg. For both bodies, the optimal value of L(15) was
empirically derived to be ~0.65.
The lower resolution 4-color global mosaic was created separately
using the same procedures and then merged with the panchromatic
base map using the technique of [MCEWEN1991] to produce a
global 4-color full-resolution map of Pluto and Charon.
/color: 4-color Image Cubes for Pluto and All Satellites
--------------------------------------------------------
These products contain MVIC data converted to I/F and reprojected to
the perspective view of the target as seen from the spacecraft at the
mid-scan header time for the BLUE filter scan, for each MVIC color
scan where the target is well resolved and well lit.
For each scan, the reprojected spatial resolution is selected to be
somewhat higher than the resolution of the raw data, so as not to lose
detail in the reprojection. After all 4 filters have been reprojected
to the same geometry, they are stacked into an IMG file with
dimensions [nx,ny,4] where nx and ny are spatial dimensions oriented
such that north is up, and the four filters are in the order listed in
the instrument description above.
An additional correction was applied to the CH4 filter, relative to
that described in the Howett et al. paper, of 0.938, empirically
determined from the Charon scans to make CH4 I/F match that of NIR.
This correction was based on the understanding that Charon's Pluto-
facing hemisphere is neutral in color at MVIC's NIR and CH4
wavelengths, as reported in [FINKETAL1988].
File naming convention:
Target identity is indicated by the letters 'pl' for Pluto or 'ch'
for Charon in the filename. The 0x545 and 0x536 tags identify the
raw packet id (ApID). Scan identity is indicated by MET unique
identifiers (10-digit integers indicating mission elapsed time in
seconds). In many cases, a single scan covers Pluto and Charon,
leading to two sets of products. The observations included in this
dataset are listed here:
MET_id Descriptive_name Target
-----------------------------------------
298719172 PC_MULTI_MAP_B_5 Pluto
298766872 PC_MULTI_MAP_B_6 Pluto
298824437 PC_MULTI_MAP_B_8 Pluto
298853042 PC_MULTI_MAP_B_9 Pluto
298853042 PC_MULTI_MAP_B_9 Charon
298853212 PC_MULTI_MAP_B_9 Pluto
298853212 PC_MULTI_MAP_B_9 Charon
298891582 PC_MULTI_MAP_B_11 Pluto
298891582 PC_MULTI_MAP_B_11 Charon
298939122 PC_MULTI_MAP_B_12 Pluto
298939122 PC_MULTI_MAP_B_12 Charon
298939292 PC_MULTI_MAP_B_12 Pluto
298939292 PC_MULTI_MAP_B_12 Charon
298995294 PC_MULTI_MAP_B_14 Pluto
298995294 PC_MULTI_MAP_B_14 Charon
299025872 PC_MULTI_MAP_B_15 Pluto
299025872 PC_MULTI_MAP_B_15 Charon
299064592 PC_MULTI_MAP_B_17 Pluto
299064592 PC_MULTI_MAP_B_17 Charon
299079022 PC_MULTI_MAP_B_18 Pluto
299079022 PC_MULTI_MAP_B_18 Charon
299104952 PCNH_Multi_Long_1d1_01 Pluto
299104952 PCNH_Multi_Long_1d1_01 Charon
299127622 PC_Multi_Long_1d2 Pluto
299127622 PC_Multi_Long_1d2 Charon
299147977 PC_Color_TimeRes Pluto
299147977 PC_Color_TimeRes Charon
299162512 PC_Color_1 Pluto
299162512 PC_Color_1 Charon
299176432 C_COLOR_2 Charon
299178092 P_COLOR2 Pluto
-----------------------------------------
The highest resolution Pluto and Charon products from this
dataset have also been presented in [GRUNDYETAL2016A],
[STERNETAL2015], [MOOREETAL2016], and [GRUNDYETAL2016B],
but this dataset was created from later MVIC products using the
most recent SPICE kernels.
(SPICE is a toolkit provided by the Jet Propulsion Laboratory
Navigation and Ancillary Information Facility, and it stands for
Spacecraft ephemeris, Planet or any target body ephemeris and physical
constants, Instrument information, C-matrix attitude and orientation
information, and Events information).
Processes for converting to I/F and mutually registering the separate
color channels for Pluto and Charon are the same as described in the
references above. A different process was used for the smaller moons
and is described below.
To co-register cubes for Nix and Hydra using MVIC scans, three
well-resolved color scans from the raw dataset were converted
into cubes:
SAPNAME File_Root Power_Side
H_Color_Best 0299165322_0x536_eng.fit 0
N_COLOR_BEST 0299166912_0x536_eng.fit 0
N_Color_2 0299171078_0x536_eng.fit 1
The engineering files were then debiased, electronic stripe
noise was removed, and the data was flat-fielded. The following
flat fields were applied, from the calibrated dataset:
mc0_flat_20160120.fits
mc1_flat_20160120.fits
mc2_flat_20160120.fits
mc3_flat_20160120.fits
The destriped, flat-fielded files were then windowed to
approximately 5x the width of the target. These windowed files
were co-registered across the four MVIC color filters (Blue, Red,
NIR, and CH4) at a sub-pixel level using the following approach.
Each of the files from a given scan were scaled up in dimension by
a factor of 6 using bilinear interpolation. The upscaled, windowed
Red band image for each scan were chosen as the template for
co-registration. For each of the other three frames to be
co-registered to the Red frame, a mean flux scaling factor, Fs,
was determined by computing the sum of the given channel to the
sum of the Red channel. The best integer x and y pixel offsets
for channel i was determined by brute-force minimizing:
CHI = sum( (Fs*Im_Red - shift(Im_i, x, y))^2 / (Im_i + eps))
In the formula above, shift(Im, x, y) is the channel i image after
linear integer pixel shifts of x and y, and eps is a small flux
offset to account for noise from removed sky and read noise. For
these scans, eps was set to 5.0 DN.
Once the upscaled images were co-registered, the images were
re-sampled with a mean block-reduce function to their original
pixel scale. The resulting co-registered images from a given scan
were assembled into a FITS cube with the original file headers
included in each extension. Units are in native MVIC DN.
No power side correction was applied to N_Color_2, as tests
comparing it to N_COLOR_BEST indicate that the NIR channel gain
drift amplitude was <1 percent for this scan.
No attempt was made to match PSFs between the four channels; as
such, there are limb artifacts in RGB composites of the cubes due
to the narrower PSF of the Blue channel with respect to the
longer-wavelength channels.
/spec: 1.25-2.5 Micron Image Cubes for Pluto and Satellites
------------------------------------------------------------
This dataset contains spatial - spectral I/F cubes of scans
across Pluto, Charon, Nix, Hydra, and Kerberos from the LEISA
instrument in three dimensions, nx, ny, and nw. The first two
dimensions (nx and ny) are spatial dimensions to cover the
mid-scan-time field of view centered on the target. The third axis
(nw) has 256 channels across the wavelength range of 1.25 to 2.5
microns, with a high resolution section in channels 200 to 255 for
wavelengths between 2.10 and 2.25 microns. The associated
wavelength product is needed when using this data because the
wavelength response of each row of LEISA pixels is slightly
curved, referred to as the spectral smile. Associated
geometry products contain the approximate geometry as of the
mid-scan time. The starting MET of the scan is included as
part of the filename. On LEISA there is a glue bond between the high
resolution segment and the low resolution segment. There is scattered
light off of the glue bond that affects the signal that reaches
channels 199-207 (the last channel of the low resolution section and
the first 8 channels of the high resolution segment). The scattered
light pattern is not uniform across the detector because there are
chips along the glue bond that make it not uniform. Observations were
designed to have the target avoid the worse areas of scattered light.
LEISA operates in a pushbroom fashion, where each row of the
LEISA frame is a different wavelength. The LEISA frames are
used to construct an image cube where each plane of the cube
represents a single wavelength.
LEISA's 256x256 HgCdTe detector array has linear-variable
interference filters affixed to it that cover wavelengths from
1.25 to 2.5 microns. The filters are oriented such that one axis
of the detector array is mostly spatial and the other axis is
both spatial and spectral. The field of view is swept across the
scene of interest while recording frames at a rate of approximately
one frame per pixel of motion. The resulting sequences of frames
are provided as level 1 and level 2 data.
Making optimal use of the lower level data requires knowledge of
the time history of the spacecraft orientation. This history is
incorporated to produce the higher level data products in this
directory. These products are produced using the USGS's Integrated
Software for Imagers and Spectrometers, ISIS3, which accounts for
camera geometry and for spacecraft orientation as a function of
time during the spectral scan, providing a footprint on-or-off of
the target for each pixel of each LEISA frame. These footprints
are reprojected by the software to the mid-scan view from the
spacecraft to produce spectral cubes, as tabulated below.
Scans of Pluto:
MET Scan name UT date and time Range(km) SubSClon&lat
-------------------------------------------------------------------------
0299026199 PC_MULTI_MAP_B_15 2015-07-12 17:01:49 2123418 247.35 42.92
0299064869 PC_MULTI_MAP_B_17 2015-07-13 03:46:32 1589686 222.26 42.86
0299079314 PC_MULTI_MAP_B_18 2015-07-13 07:46:25 1391154 212.94 42.82
0299105209 PCNH_MULTI_LONG_1d1 2015-07-13 14:59:33 1032784 196.19 42.70
0299127869 PC_MULTI_LONG_1d2 2015-07-13 21:18:58 718986 181.68 42.49
0299144829 P_LEISA 2015-07-14 02:01:50 468610 170.42 42.12
0299169338 P_LEISA_Alice_1a 2015-07-14 08:48:06 149717 158.78 39.72
0299170159 P_LEISA_Alice_1b 2015-07-14 09:00:36 139431 158.66 39.42
0299172014 P_LEISA_Alice_2a 2015-07-14 09:33:05 112742 158.62 38.52
0299172889 P_LEISA_Alice_2b 2015-07-14 09:48:16 100297 158.81 37.91
0299176809 P_LEISA_HIRES 2015-07-14 10:56:19 45222 164.17 30.73
-------------------------------------------------------------------------
Scans of Charon:
MET Scan name UT date and time Range(km) SubSClon&lat
-------------------------------------------------------------------------
0299026199 PC_MULTI_MAP_B_15 2015-07-12 17:01:49 2129381 66.70 42.78
0299064869 PC_MULTI_MAP_B_17 2015-07-13 03:46:32 1600665 41.64 42.49
0299079314 PC_MULTI_MAP_B_18 2015-07-13 07:46:25 1403516 32.38 42.35
0299105209 PCNH_MULTI_LONG_1d1 2015-07-13 14:59:33 1046821 15.83 42.00
0299127869 PC_MULTI_LONG_1d2 2015-07-13 21:18:58 733569 1.67 41.46
0299146219 C_LEISA 2015-07-14 02:21:50 483075 351.00 51.55
0299171308 C_LEISA_LORRI_1 2015-07-14 09:20:28 137829 342.40 34.15
0299175509 C_LEISA_HIRES 2015-07-14 10:32:06 80651 346.38 27.17
-------------------------------------------------------------------------
Each of the above scans is converted to an array with dimensions
[nx,ny,nw] where nx and ny are spatial dimensions to cover the
mid-scan-time field of view centered on the target at 2 to 3 times
the native LEISA resolution. The third axis nw is LEISA's 256
wavelength channels. Values in the arrays are I/F for pixels that
fall on the target, or -3.4028235e-38 for pixels that are off the
target or are bad for other reasons (unpatchable cosmic rays, dead
pixels, etc.). Channels 0-196 cover wavelengths from 1.25 to 2.5
microns at low spectral resolution. Channels 200-255 cover
wavelengths from 2.10 to 2.25 microns at higher spectral resolution,
but with highly uncertain flux calibration, mostly due to confusion
from light scattering through the glue bond between the low res and
high res wavelength segments.
Accompanying each Pluto/Charon I/F cube is a wavelengths array with
the same [nx,ny,nw] dimensions providing the wavelength for each
pixel. This array is needed because the wavelength response of each
row of LEISA pixels is not quite constant, but exhibits a slight
curvature, referred to as the spectral smile. To account for this
effect, use the wavelengths from the accompanying wavelengths array.
A third array describes the geometry as of the mid-scan time (the
times in the table above). This array has dimensions [nx,ny,ng],
where the number of geometry planes ng is 5, in this order: phase
angle, emission angle, incidence angle, latitude, and longitude
(all angles in degrees). The finite duration of the scan means the
geometry array is only approximate. If you need the exact geometry
for each pixel, then this product is not what you need. Instead,
go back to the level 1 or level 2 data along with the spacecraft
orientation time history data recorded in the relevant SPICE
kernels.
For Nix, Kerberos, and Hydra, the LEISA images taken at the listed MET
were used for these data products:
MET Target Date MidObsTime Distance Duration ExpTime PixScale Phase
(s) (UT) (UT) (km) (s) (s) (km/pix) (deg)
----------------------------------------------------------------------------
0299153775 Kerb. 2015-07-14 04:27:16.375 394,000 359 0.868 24.2 24.81
0299154901 Hydra 2015-07-14 04:46:51.875 369,000 458 0.969 22.7 26.48
0299164549 Hydra 2015-07-14 07:28:01.876 239,000 502 0.854 14.7 33.05
0299166335 Nix 2015-07-14 07:56:26.876 163,000 340 0.676 10.0 8.65
0299173908 Nix 2015-07-14 10:04:04.376 60,000 509 0.579 3.7 9.65
----------------------------------------------------------------------------
The images for Nix, Hydra, and Kerberos are processed differently
from the Pluto and Charon scans and do not include geometry
information. They are cube FITS files with the data in the first
object plus 4 extensions. From extension number 1 to 4, they are the
wavelength, estimated error, gains and flat field.
New Horizons made LEISA observations of all small satellites
of Pluto except Styx. This dataset contains observations
covering the near-IR range from 1.25 to 2.5 microns at a
resolving power of ~260, and from 2.10 to 2.25 microns at a
resolving power of ~520. Each LEISA frame has been
flat-fielded using the v4 LEISA flat field, corrected for
background pattern noise and calibrated to I/F.
The processing uses the pointing history of the spacecraft,
from housekeeping data, to correct for the target's motion
within the LEISA frames.
/absorp: Reprojected LEISA Absorption Maps of Pluto
----------------------------------------------------
This dataset includes four band depth and spectral indicator
maps of Pluto from the LEISA hyperspectral imager, in simple
cylindrical projection:
- CH4 integrated band depth maps of the band group around 1.7
micrometers
- N2 integrated band depth maps of the 2.150 micrometer band
- CO integrated band depth maps of the 1.578 micrometer band
- H2O spectral indicator (2.06 / 1.39 micrometers)
They are respectively provided in the files:
- leisa_809-889-014_band-ch4_i89.img
- leisa_889-014_band-n2_i88.img
- leisa_889-014_band-co_i88.img
- leisa_809-889-014_si-h2o_norm_i89.img
Values outside valid ranges have been set to '-99'.
Band depths & spectral indicator calculations are in their
native observation geometry, with 2 km/pix (at image center)
re-sampled data for both P_LEISA_Alice_2a/b observations and
1 km/pix for P_LEISA_HIRES.
The maps were then projected as simple cylindrical maps with
a common 0.0482 degrees/pix resampling corresponding to 1 km/pix
sampling at the equator. The data were then mosaicked with the high
resolution swath overlaid over the two others.
The observations included in these maps are:
-----------------------------------------
MET_id Descriptive_name Target Resolution Maps
------------------------------------------------------------------
0299172014 P_LEISA_Alice_2a Pluto 6.95 km CH4, N2, CO, H2O
0299172889 P_LEISA_Alice_2b Pluto 6.20 km CH4, N2, CO, H2O
0299176809 P_LEISA_HIRES Pluto 2.75 km CH4, H2O
This dataset uses calibration version 'v5', with flat field '4x'.
The two first observations together cover most of the illuminated
hemisphere of Pluto at the time just before the closest flyby while
the high resolution swath covers a strip about 700 km wide and 2700
km long, going from the SSE of the illuminated hemisphere to its W
side. In the CH4 and H2O maps, this high resolution swath is
overlaid over the two others.
Note: In some of the maps residual calibration artifacts inside the
observations and small mismatches in intensity between the individual
observations, with a linear structure in the original projection,
produce the curved structures seen in the cylindrical maps, mostly
apparent in the N2 and CO maps (weak bands), and very faintly in the
CH4 map. The flat was made from a sideways scan across Pluto, so
Pluto's spectral features have to be removed from it.
Details:
- CH4 map:
This map plots the integrated CH4 band depth between 1.589 and
1.833 micrometers (um) over a group of 3 CH4 bands at about 1.67,
1.72, and 1.79 um. Its integrate the reflectance factor between a
continuum estimated around Wavelength_1=1.589 um (5 bands average)
and around Wavelength_2=1.833 um (3 bands average). The full
equation is provided in eq. 1 of [SCHMITTETAL2017] and also here:
(where lam = lambda = wavelength):
BD(CH4) = 1 - Integral(from lam1 to lam2) RF(lam)dlam /
Integral(from lam1 to lam2) Cont(lam)dlam
The CH4 band depth intensity of the high resolution map
(P_LEISA_HIRES) has been slightly shifted (8 percent) and
stretched (10 percent) to best fit the values of the other
observations.
The signal-to-noise ratio has been greatly improved using the
global principal component analysis (PCA) covering most of the
LEISA spectral range and spectrum reconstruction with inverse
PCA. This analysis has been limited to incidence and emergence
angles below 89 degrees. Since the band is very strong, the
signal to noise ratio (S/N)
is very high and the band depth is very sensitive, a minimum
detection threshold of 0.0 is safe to use. Negative values
means no CH4 was detected, although some very weak CH4 bands
are still detected in H2O-dominated or Red material-dominated
areas down to band depth, about -0.05. The maximum value in
the image is about 0.55.
- N2 map:
This map plots the integrated N2 band depth between 2.136 and
2.160 micrometers over the N2 band at about 2.15 um.
The full equation is provided in eq. 2 of [SCHMITTETAL2017] and
reproduced here:
BD(N2) = 1 - [RF(2.136um) + RF(2.144um) +
RF(2.152um) + RF(2.160um)] / [RF(2.121um) + RF(2.1285um) +
RF(2.1675um) + RF(2.1755um)].
The signal-to-noise ratio has been greatly improved using a
specific PCA around the 2.15 micrometer band and spectrum
reconstruction with inverse PCA. This analysis has been limited to
incidence angles below 88 degrees and emergence angles below 89
degrees. This band being weak, the S/N is low, and a global
minimum detection threshold of about 0.025 should be used. The
local detection threshold can be lower (~0.01). Negative values
mean no N2 was detected. The maximum value in the image is 0.228.
As demonstrated in details in [SCHMITTETAL2017], the N2 band
depth depends on the fraction of the pixel covered by N2 ice but
does not depend on the proportion of N2 (mostly over 95-99
percent).
This band depth is sensitive to the grain size, but is inversely
sensitive to the amount of CH4 dissolved in it, and can be hidden
completely when more than about 1 percent of CH4 is present. So a
significant part of Pluto's surface still contains N2 ice but
cannot be mapped with the N2 band depth.
- CO map:
This map plots the integrated CO band depth between 1.566 and
1.578 micrometers (um) over the CO band at about 1.58 um (2 nu).
The full equation is: BD(CO) = 1 - [RF(1.5665um) + RF(1.572um)
+ RF(1.578um)] / [1.5 * [RF(1.561um)+ RF(1.583um)]]
(Eq. 3 in [SCHMITTETAL2017]), but this calculation has been
shifted to have a center at 1.572 um instead of 1.578 um (one
spectel) to try to overcome the smile effect.
A specific PCA around the 1.578 micrometer band and spectrum
reconstruction with inverse PCA has greatly improved the
signal-to-noise ratio. This analysis has been limited to
incidence angles below 88 deg and emergence angles below 89 deg.
However, this band is very weak and narrow, its intensity
is very sensitive to the 'spectral smile' affecting the data
(not yet corrected) and the relative intensity of the band
at large scale can be very strongly perturbated. The CO
locations are relatively fiable but some areas, especially
to the E of Pluto may be missing. A minimum threshold of
about 0.005 should be used as the signal to noise is also low.
Negative values means no CO was detected.
- H2O map:
This map plots a specially designed H2O spectral indicator using
10 wavelength bands around each of 1.39 and 2.06 micrometers as
defined in eq. 4 of [SCHMITTETAL2017] to improve the signal to
noise ratio, given here again:
SI(H2O) = 1 - SUM[RF(2.022um) to RF(2.090um)] /
SUM[RF(1.365um) to RF(1.410um)]
It was found the most sensitive for separating H2O from the
signature of the Red material and also for maximizing the
contrast with CH4 ice.
This spectral indicator, mainly spanning the [-0.25 - 0.65]
range, has been normalized between [0 - 1] for easier use.
Negative values means no H2O was detected. The initial
detection threshold of the high resolution map (P_LEISA_HIRES)
has been slightly upshifted to -0.20 before normalization, to
best fit the values of the other observations.
The presence of red material may affect the low values (< 0.25)
of this normalized H2O spectral indicator. This map did not
use the MVIC 'red slope' to conservatively remove this effect
(see Schmitt et al. 2017) as this slope indicator is not yet
available as a global map.
More detailed information is provided in [SCHMITTETAL2017].
Contact Information
===================
For any questions regarding the data format of the archive,
contact
New Horizons RALPH Principal Investigator:
Alan Stern, Southwest Research Institute
S. Alan Stern
Southwest Research Institute
Department of Space Studies
1050 Walnut Street, Suite 400
Boulder, CO 80302
USA
|
.png)
.png)
