6,042 research outputs found
Four dimensional studies in earth space
A system of reference which is directly related to observations, is proposed for four-dimensional studies in earth space. Global control network and polar wandering are defined. The determination of variations in the earth's gravitational field with time also forms part of such a system. Techniques are outlined for the unique definition of the motion of the geocenter, and the changes in the location of the axis of rotation of an instantaneous earth model, in relation to values at some epoch of reference. The instantaneous system referred to is directly related to a fundamental equation in geodynamics. The reference system defined would provide an unambiguous frame for long period studies in earth space, provided the scale of the space were specified
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. An all-sky survey of
We measure the smoothness of the infrared sky using the COBE DIRBE maps, and
obtain interesting limits on the production of the diffuse cosmic infrared
background (CIB) light by matter clustered like galaxies. The predicted
fluctuations of the CIB with the DIRBE beam size of 0.7\deg\ are of the order
of 10\%, and the maps are smooth at the level of a few
\nwm2sr rms from 2.2 to 100 \um. The lowest numbers are achieved at mid- to
far-IR where the foreground is bright but smooth; they are
\nwm2sr at 10-100 \um. If the CIB comes
from clustered matter evolving according to typical scenarios, then the
smoothness of the maps implies CIB levels less than \nwm2sr
over this wavelength range.Comment: 15 pages (LATEX) with 2 figures and 1 plate; Ap. J. Letters, in pres
The analysis of temporal variations in regional models of the Sargasso Sea from GEOS-3 altimetry
The dense coverage of short pulse mode GEOS-3 altimeter data in the western North Atlantic provides a basis for studying time variations in the sea surface heights in the Sargasso Sea. Two techniques are utilized: the method of regional models, and the analysis of overlapping passes. An 88 percent correlation is obtained between the location of cyclonic eddies obtained from infrared imagery and sea surface height minima in the altimeter models. This figure drops to 59 percent in the case of correlations with maxima and minima of surface temperature fields. The analysis of overlapping passes provides a better picture of instantaneous sea state through wavelengths greater than 30 km. The variability of the Sargasso Sea through wavelengths between 150 km and 5000 km is estimated at + or - 28 cm. This value is in reasonable agreement with oceanographic estimates and is compatible with the eddy kinetic energy of a wind driven circulation
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. I. and limits on the near-IR background
This paper is devoted to studying the CIB through its correlation properties.
We studied the limits on CIB anisotropy in the near IR (1.25, 2.2, and 3.5 \um,
or ) bands at a scale of 0.7\deg\ using the COBE\footnote{ The
National Aeronautics and Space Administration/Goddard Space Flight Center
(NASA/GSFC) is responsible for the design, development, and operation of the
{\it COBE}. Scientific guidance is provided by the {\it COBE} Science Working
Group. GSFC is also responsible for the development of the analysis software
and for the production of the mission data sets.} Diffuse Infrared Background
Experiment (DIRBE) data. In single bands we obtain the upper limits on the
zero-lag correlation signal \w2m4sr2 for the
bands respectively. The DIRBE data exhibit a clear color between the
various bands with a small dispersion. On the other hand most of the CIB is
expected to come from redshifted galaxies and thus should have different color
properties. We use this observation to develop a `color subtraction' method of
linear combinations of maps at two different bands. This method is expected to
suppress the dominant fluctuations from foreground stars and nearby galaxies,
while not reducing (or perhaps even amplifying) the extragalactic contribution
to . Applying this technique gives significantly lower and more isotropic
limits.Comment: 44 pages postcript; includes 5 tables, 14 figures. Astrophysical
Journal, in pres
On the unification of geodetic leveling datums using satellite altimetry
Techniques are described for determining the height of Mean Sea Level (MSL) at coastal sites from satellite altimetry. Such information is of value in the adjustment of continental leveling networks. Numerical results are obtained from the 1977 GEOS-3 altimetry data bank at Goddard Space Flight Center using the Bermuda calibration of the altimeter. Estimates are made of the heights of MSL at the leveling datums for Australia and a hypothetical Galveston datum for central North America. The results obtained are in reasonable agreement with oceanographic estimates obtained by extrapolation. It is concluded that all gravity data in the Australian bank AUSGAD 76 and in the Rapp data file for central North America refer to the GEOS-3 altimeter geoid for 1976.0 with uncertainties which do not exceed + or - 0.1 mGal
New measurements of cosmic infrared background fluctuations from early epochs
Cosmic infrared background fluctuations may contain measurable contribution
from objects inaccessible to current telescopic studies, such as the first
stars and other luminous objects in the first Gyr of the Universe's evolution.
In an attempt to uncover this contribution we have analyzed the GOODS data
obtained with the Spitzer IRAC instrument, which are deeper and cover larger
scales than the Spitzer data we have previously analyzed. Here we report these
new measurements of the cosmic infrared background (CIB) fluctuations remaining
after removing cosmic sources to fainter levels than before. The remaining
anisotropies on scales > 0.5 arcmin have a significant clustering component
with a low shot-noise contribution. We show that these fluctuations cannot be
accounted for by instrumental effects, nor by the Solar system and Galactic
foreground emissions and must arise from extragalactic sources.Comment: Ap.J.Letters, in pres
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