NSSDCA ID: ASIR-00002
Availability: Archived at NSSDC, accessible from elsewhere
Time span: 1989-12-22 to 1991-12-22
The COBE DMR Project Data Sets (PDS) include Sky Maps and Pixelized Differential Data. In addition, there are five Analyzed Science Data Sets. All of these data are presented in FITS binary tables.
There are six PDS Sky Maps, corresponding to the two independent channels and three frequencies (31.5, 53, and 90 GHz) of the COBE Differential Microwave Radiometers (DMR). The maps are quadrilateralized spherical projections in ecliptic coordinates. A sparse matrix least squares minimization technique was used to derive, from highly redundant sky sampling, a differential temperature for each of 6144 map pixels while simultaneously allowing for instrumental and systematic effects. The 53 and 90 GHz maps are comprised of data obtained during the first two years of COBE operation (22 December 1989 to 22 December 1991); the 31 GHz maps present data obtained during the same period but excluding the "eclipse seasons" (21 May - 25 July) during which the orbit of COBE crossed the Earth's shadow and the 31 GHz channels were affected by temperature and electronic changes. The observations are made with a 7 degree beam and presented in 2.8 degree pixels. Due to the differential nature of the observations, the maps have unconstrained antenna temperature zero points. While the dipole anisotropy has been removed to first order from the Sky Maps, emission from the Galaxy remains.
The DMR Analyzed Science Data Sets (ASDS) include Galactic Emission Maps and Cosmic Emission Maps. The latter result when the Galactic emission is removed. The modeled Galactic components are synchrotron emission, free-free emission, and thermal dust emission. Two techniques were used to produce the Cosmic Emission Maps, a "subtraction technique" in which the Galactic components are subtracted from the DMR maps, and a "combination technique" in which a linear combination of the DMR maps is used to cancel the Galactic emission.
The calibrated differential antenna temperature (DT) and the number of observations are given for each combination of sky positions observed simultaneously by a DMR horn pair in Pixelized Differential Data files. The data (temperature in "horn 1" minus temperature in "horn 2") are sorted according to the COBE sky map pixel number seen by horn 1, and sub-sorted by the horn 2 pixel number. The observations are made with a 7 degree beam and presented in 2.8 degree pixels. All differential temperatures for a given pixel pair are combined, after correcting for known systematic errors and subtracting a nominal dipole to minimize pixel gradient effects, into four moment sums, specifically the sums of DT, (DT)^2, (DT)^3, and (DT)^4. There are six Pixelized Differential Data files corresponding to two independent DMR channels at each of the three observed frequencies. Each file is about 40 MB in size. The Pixelized Differential Data Sets describe observations made during the same two-year period as the PDS Sky Maps.
Detailed descriptions of the data products are given in separate Explanatory Supplements for the Project Data Sets and Analyzed Science Data Sets.
Questions and comments about this data collection can be directed to: Dr. David T. Leisawitz
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Charles L. Bennett | Data Provider | NASA Goddard Space Flight Center | bennett@map.gsfc.nasa.gov |