JOHNS HOPKINS UNIVERSITY SPECTRAL LIBRARY 

With the exception of manmade materials, all spectra in the Johns
HopkinsLibrary were measured under the direction of John W. (Jack)
Salisbury. Mostmeasurements were made by Dana M. D'Aria, either at Johns
Hopkins Universityin Baltimore, MD, or at the U.S. Geological Survey in
Reston, VA. 

This text is a general introduction to the library, with an overview
ofMeasurment techniques, which do differ for different materials. There
is a separate introductory text for each kind of material (rocks,
minerals, lunar soils, terrestrial soils, manmade materials, meteorites,
vegetation, snow&amp;ice, etc.) that contains more specific information
pertinent to that material. 

Any questions concerning the Johns Hopkins Library can be e-mailed to
Jack Salisbury at salisburys@worldnet.att.net. 

MEASUREMENT TECHNIQUE 

Two different kinds of spectral data are resident in this library.
Spectra of minerals and meteorites were measured in bidirectional
(actually biconical reflectance (see two Salisbury et al., 1991
references below for details). 

These spectra, recorded from 2.08-25 micrometers, cannot be used to
quantitatively predict emissivity because only hemispherical
reeflectance can be used in this way. However, when recorded properly,
as described in the meteorite paper, curve shape is accurate enough for
remote sensing applications. 

All other spectral data, with the exception of portions of generic snow
and vegetation spectra (see the introductory text for each type of
material), were measured in directional hemispherical reflectance. Under
most conditions, the infrared portion of these data can be used to
calculate emissivity using Kirchhoff's Law (E=1-R), which has been
verified by both laboratory and field measurements (Salisbury et al.,
1994; Korb et al., 1996). The unusual circumstances (e.g., the lunar
environment) where thermal gradients may cause significant departure
from Kirchhoffian behavior are discussed in Salisbury et al., 1994. 

The apparently seamless reflectance spectra from 0.4 to 14 micrometers
of Rocks and soils were generated using two different instruments, both
equipped with integrating spheres for measurement of directional
hemispherical reflectance, with source radiation impinging on the sample
from a centerline angle 10 degrees from the vertical. 

Unless specified otherwise (see relevant introductory texts for generic
snow and vegetation spectra, and spectra of manmade materials), all
visible/near-infrared (VNIR) spectra were recorded using a Beckman
Instruments model UV 5240 dual-beam, grating spectrophotometer at the
U.S. Geological Survey, Reston, VA. The data were obtained digitally and
corrected for both instrument function and the reflectance of the Halon
reference using standards traceable to the U. S. National Institute of
Science and Technology. Measurements of such standards indicate an
absolute reflectance accuracy of plus or minus 3 percent. Wavelength
accuracy was checked using a holmium oxide reference filter and is
reproducible and accurate to within plus or minus 0.004 micrometers, or
4 nm (one digitization step). Spectral resolution is variable because
the Beckman uses an automatic slit program to keep the energy on the
detector constant. The result is a spectral bandwidth typically less
than 0.008 micrometers over the 0.4 to 2.5 micrometers spectral range
measured, but slightly larger at the two extremes of the range of the
lead sulfide detector (0.8-0.9 micrometers and 2.4- 2.5 micrometers).
This instrument has a grating change at 0.8 micrometers, which sometimes
results in a spectral artifact (either a small, sharp absorption band,
or a slight offset of the spectral curve) at that wavelength. 

Two similar instruments were used to record reflectance in the infrared
range (2.08 to 15 micrometers). Briefly, both are Nicolet FTIR
spectrophotometers and both have a reproducibility and absolute accuracy
better than plus or minus 1 percent over most of the spectral range.
Early measurements of igneous rocks with an older detector were noisy in
the 13.5-14 micrometers range and do not quite meet this standard in
that region. Because FTIR instruments record spectral data in frequency
space, both wavelength accuracy and spectral resolution are given in
wavenumbers (reciprocal centimeters). Wavelength accuracy of an
interferometer type of instrument is limited by the spectral resolution,
which yields a data point every 2 wavenumbers for these measurements.
The X-axis was changed from wavenumbers to micrometers for all of these
data before the infrared segment was joined to the VNIR data from the
Beckman. 

Spectra from the Beckman and the FTIR instruments were compared in
theoverlap range of 2.08-2.5 micrometers. If the difference was greater
than 3 percent, measurements were repeated. Typically, however, the
agreement was within the 3 percent limit. In view of the greater
accuracy of the FTIR measurements, any small discrepancy between the two
spectral segments was resolved by adjusting the Beckman data to fit the
reflectance level of thesegment measured by the FTIR instruments. 

Recent publications describing and interpreting spectral data in the
library, as well as some spectral data not yet included, are listed
below. 

REFERENCES AND RECENT PUBLICATIONS 

Clark, B. E., Fanale, F. P., and Salisbury, J. W., 1992,
Meteorite-asteroid Spectral comparison: The effects of comminution,
melting, and recrystallization: Icarus, v. 97, p. 288-297. 

Korb, A. R., Dybwad, P., Wadsworth, W., and Salisbury, J. W., 1996,
1996, Portable FTIR spectrometer for field measurements of radiance and
emissivity: Applied Optics, v. 35, p. 1679-1692. 

Nash, D. B. and Salisbury, J. W., 1991, Infrared reflectance spectra of
plagioclase feldspars: Geophysical Research Letters, V 18, p. 1151-1154.

Rowan, L. C., Salisbury, J. W., Kingston, M. J., Vergo, N.S. and
Bostick, N. H., 1991, Evaluation of visible, near-infrared and
thermal-infrared reflectance spectra for studying thermal alteration of
Pierre shale, Wolcott, Colorado: Journal of Geophysical Research V96, p.
18,047-18,057. 

Salisbury, J. W., D'Aria, D. M., and Jarosevich, E., 1991a, Midinfrared
(2.5-13.5 micrometers) reflectance spectra of powdered stony meteorites:
Icarus, v. 92, p. 280-297. 

Salisbury, J. W., Walter, L. S., Vergo, N., and D'Aria, D. M., 1991b,
Infrared (2.1- 25 micrometers) Spectra of Minerals: Johns Hopkins
University Press, 294 pp. 

Salisbury, J. W. and Wald A. E., 1992, The role of volume scattering in
Reducing spectral contrast of reststrahlen bands in spectra of powdered
minerals: Icarus, v. 96, p. 121-128. 

Salisbury, J. W. and D'Aria, D. M., 1992, Infrared (8-14 µm) remote
sensing of soil particle size: Remote Sensing of Environment, v. 42, p.
157-165. 

Salisbury, J. W. and D'Aria, D. M., 1992, Emissivity of terrestrial
materials in the 8-14 µm atmospheric window: Remote Sensing of
Environment, v. 42, p. 83-106. 

Salisbury, J. W., 1993, Mid-infrared spectroscopy laboratory data:
Chapter 4 in Remote Geochemical Analysis, C. M. Pieters and P. A. J.
Englert eds., Cambridge University Press, New York, p. 79-98. 

Salisbury, J. W., D'Aria, D. M. and Sabins, F. F., 1993, Thermal
infrared Remote sensing of crude oil slicks: Remote Sensing of
Environment, v. 45, p. 225-231. 

Salisbury, J. W., and D'Aria, D. M., 1994, Emissivity of terrestrial
materials in the 3-5 µm atmospheric window: Remote Sensing of
Environment, v. 47, p. 345-361. 

Salisbury, J. W., D'Aria, D. M., and Wald, A., 1994, Measurements of
thermal infrared spectral reflectance of frost, snow, and ice: Jour. of
Geophys. Res., v. 99, p. 24,235-24,240. 

Salisbury, J. W., Wald, A., and D'Aria, D. M., 1994, Thermal-infrared
remote sensing and Kirchhoff's law 1. Laboratory measurements: Jour. of
Geophysical Research, v. 99, p. 11,897-11,911. 

Salisbury J. W., Murcray, D. G., Williams, W. J., and Blatherwick, R.
D., 1995, Thermal infrared spectra of the Moon: Icarus, v. 115, p.
181-190. 

Salisbury, J. W., Basu, A., and Fischer, E. M., 1997, Thermal infrared
spectra of lunar soils: submitted to Icarus, March, 1997. 

Thompson, J. L., and Salisbury, J. W., 1993, The mid-infrared
reflectance of mineral mixtures (7-14 µm): Remote Sensing of
Environment, v. 45, p. 1-13. 

Wald, A. É. and Salisbury J. W., 1992, Angular dependence of spectral
Emissivity of quartz and basalt: (Extended abstract) Twenty-third Annual
Lunar and Planetary Science Conference, p. 1485-1486. 

Wald, A. E., and Salisbury, J. W., 1995, The thermal infrared
directional emissivity of powdered quartz: Jour. of Geophys. Res., v.
100, p. 24,665-24675.
