DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset is comprised of asteroid flux data measured in 26 filters
using the McCord dual beam photometer. Of the 26 filters used for the
full dataset, a maximum of 24 were used for any one measurement. The
wavelength range covered is from 0.32 to 1.08 microns.
Processing Level Id : 3
Software Flag : N
Processing Start Time : 1975
Processing Stop Time : 1984
Parameters
==========
Sampling Parameter Name : WAVELENGTH
Data Set Parameter Name : FLUX RATIO
Minimum Sampling Parameter : 0.330000
Maximum Sampling Parameter : 1.100000
Data Set Parameter Unit : DIMENSIONLESS
Noise Level : 2.000000
Sampling Parameter Unit : MICROMETER
Data
====
FLUX RATIO is defined as the ratio of two measured photon fluxes from a
photometric or spectrometric instrument. For instance, the ratio of the
measured spectrum of a target relative to the measured spectrum of a
calibration standard will yield a value that is a flux ratio. This
parameter is dimensionless.
Ancillary Data
==============
Atmospheric Conditions
----------------------
An estimate of the quality of the observing conditions for each night of
observing is given in the original papers, Chapman (1972) [CHAPMAN1972],
Chapman and Gaffey (1979) [CHAPMAN&GAFFEY1979A] [CHAPMAN&GAFFEY1979B] and
McFadden et al. (1984) [MCFADDENETAL1984].
Calibration Standard
--------------------
The data are calibrated to flux ratio (asteroid/inferred sun) with
reference to a set of standard stars. During the observation sessions,
the standard stars are observed both to determine extinction corrections
in each filter and as color standards. Many of the standard stars used
are A- or B- Oke/Hayes standard stars and others of the solar type.
Modification History
====================
As part of a general review and upgrade of current asteroid data sets,
these data were reviewed and an additional format added. The following
changes were made to existing files:
o The 24color.lbl file was edited slightly for grammar and
to add the internal PDS reference keys corresponding to
the cited references.
o The asteroid number corresponding to object 1980 AA was
added to the 24color.tab file.
In addition, a program was written and used to split the 24color.tab file
into separate spectrum files for each observation, each with its own
label file. These files are named by the number and name of the
corresponding asteroid. The first two columns of each spectrum file
indicate the specific filter wavelength and FWHM used; these are followed
by the reflectance and uncertainty.
Only one object, 1685 Toro, had two observations in the main data file.
These are in separate files: '1685toro1' contains the data from Chapman &
Gaffey (1979b); '1685toro2' contains the data from McFadden, et al.
(1984).
Asteroid 1865 Cerberus, which had no data recorded in the original file,
has no individual spectrum file.
No changes were made to the recorded data values.
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CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
Acquisition of the 24 data points takes time; thus, a 24-point spectrum
can be affected by the varying light curve of the asteroid, as well as by
the changing sky conditions and instrument stability. In most, but not
all, cases, data were co-added from numerous rapid rotations of the
filter wheel. Uncertainties in the relative calibration between stars and
Alpha Lyrae may contribute an uncertainty of up to 2 percent in the
visible and 4 percent in the infrared bands. It is believed that this
uncertainty is larger than other systematic errors in the data.
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CITATION_DESCRIPTION |
Chapman, C.R., Gaffey, M., and McFadden, L., 24-color Asteroid
Survey. EAR-A-DBP-3-RDR-24COLOR-V2.1. NASA Planetary Data System,
1993.
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