The Dipole Observed in the COBE DMR Four-Year Data

The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Using the four year data set from all six channels of the COBE Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude $3.358 \pm 0.001 \pm 0.023$ mK in the direction $(l,b)=(264\deg.31 \pm 0\deg.04 \pm 0\deg.16, +48\deg.05 \pm 0\deg.02 \pm 0\deg.09)$, where the first uncertainties are statistical and the second include calibration and combined systematic uncertainties. This measurement is consistent with previous DMR and FIRAS resultsComment: New and improved version; to be published in ApJ next mont

Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy

We estimate the level of confusion to Cosmic Microwave Background anisotropy measurements caused by extragalactic infrared sources. CMB anisotropy observations at high resolution and high frequencies are especially sensitive to this foreground. We use data from the COBE satellite to generate a Galactic emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a template, we predict the microwave emission of the 5319 brightest infrared galaxies seen by IRAS. We simulate skymaps over the relevant range of frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width Half Max). Analysis of the temperature anisotropy of these skymaps shows that a reasonable observational window is available for CMB anisotropy measurements.Comment: 14 pages (LaTex source), 3 PostScript figures. Final version, to appear in ApJLetters May 1. Expanded discussion of systematic error

2-Point Correlations in the COBE DMR 4-Year Anisotropy Maps

The 2-point temperature correlation function is evaluated from the 4-year COBE DMR microwave anisotropy maps. We examine the 2-point function, which is the Legendre transform of the angular power spectrum, and show that the data are statistically consistent from channel to channel and frequency to frequency. The most likely quadrupole normalization is computed for a scale-invariant power-law spectrum of CMB anisotropy, using a variety of data combinations. For a given data set, the normalization inferred from the 2-point data is consistent with that inferred by other methods. The smallest and largest normalization deduced from any data combination are 16.4 and 19.6 uK respectively, with a value ~18 uK generally preferred.Comment: Sumbitted to ApJ Letter

Power Spectrum of Primordial Inhomogeneity Determined from the 4-Year COBE DMR Sky Maps

Fourier analysis and power spectrum estimation of the cosmic microwave background anisotropy on an incompletely sampled sky developed by Gorski (1994) has been applied to the high-latitude portion of the 4-year COBE DMR 31.5, 53 and 90 GHz sky maps. Likelihood analysis using newly constructed Galaxy cuts (extended beyond |b| = 20deg to excise the known foreground emission) and simultaneously correcting for the faint high latitude galactic foreground emission is conducted on the DMR sky maps pixelized in both ecliptic and galactic coordinates. The Bayesian power spectrum estimation from the foreground corrected 4-year COBE DMR data renders n ~ 1.2 +/- 0.3, and Q_{rms-PS} ~ 15.3^{+3.7}_{-2.8} microK (projections of the two-parameter likelihood). These results are consistent with the Harrison-Zel'dovich n=1 model of amplitude Q_{rms-PS} ~ 18 microK detected with significance exceeding 14sigma (dQ/Q < 0.07). (A small power spectrum amplitude drop below the published 2-year results is predominantly due to the application of the new, extended Galaxy cuts.)Comment: 9 pages of text in LaTeX, 1 postscript Table, 4 postscript figures (2 color plates), submitted to The Astrophysical Journal (Letters

Monitoring 2009 Forest Disturbance Across the Conterminous United States, Based on Near-Real Time and Historical MODIS 250 Meter NDVI Products

This case study shows the promise of computing current season forest disturbance detection products at regional to CONUS scales. Use of the eMODIS expedited product enabled a NRT CONUS forest disturbance detection product, a requirement for an eventual, operational forest threat EWS. The 2009 classification product from this study can be used to quantify the areal extent of forest disturbance across CONUS, although a quantitative accuracy assessment still needs to be completed. However, the results would not include disturbances that occurred after July 27, such as the Station Fire. While not shown here, the project also produced maximum NDVI products for the June 10-July 27 period of each year of the 2000-2009 time frame. These products could be applied to compute forest change products on an annual basis. GIS could then be used to assess disturbance persistence. Such follow-on work could lead to attribution of year in which a disturbance occurred. These products (e.g., Figures 6 and 7) may also be useful for assessing forest change associated with climate change, such as carbon losses from bark beetle-induced forest mortality in the Western United States. Other MODIS phenological products are being assessed for aiding forest monitoring needs of the EWS, including cumulative NDVI products (Figure 10)

Search For Unresolved Sources In The COBE-DMR Two-Year Sky Maps

We have searched the temperature maps from the COBE Differential Microwave Radiometers (DMR) first two years of data for evidence of unresolved sources. The high-latitude sky (|b| > 30\deg) contains no sources brighter than 192 uK thermodynamic temperature (322 Jy at 53 GHz). The cumulative count of sources brighter than threshold T, N(> T), is consistent with a superposition of instrument noise plus a scale-invariant spectrum of cosmic temperature fluctuations normalized to Qrms-PS = 17 uK. We examine the temperature maps toward nearby clusters and find no evidence for any Sunyaev-Zel'dovich effect, \Delta y < 7.3 x 10^{-6} (95% CL) averaged over the DMR beam. We examine the temperature maps near the brightest expected radio sources and detect no evidence of significant emission. The lack of bright unresolved sources in the DMR maps, taken with anisotropy measurements on smaller angular scales, places a weak constraint on the integral number density of any unresolved Planck-spectrum sources brighter than flux density S, n(> S) < 2 x 10^4 (S/1 Jy)^{-2} sr^{-1}.Comment: 16 pages including 2 figures, uuencoded PostScript, COBE preprint 94-0

Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer

The angular power spectrum estimator developed by Peebles (1973) and Hauser & Peebles (1973) has been modified and applied to the 4 year maps produced by the COBE DMR. The power spectrum of the observed sky has been compared to the power spectra of a large number of simulated random skies produced with noise equal to the observed noise and primordial density fluctuation power spectra of power law form, with $P(k) \propto k^n$. The best fitting value of the spectral index in the range of spatial scales corresponding to spherical harmonic indices $3 \leq \ell \lesssim 30$ is an apparent spectral index $n_{app}$ = 1.13 (+0.3) (-0.4) which is consistent with the Harrison-Zel'dovich primordial spectral index $n_{pri} = 1$ The best fitting amplitude for $n_{app} = 1$ is $\langle Q_{RMS}^2\rangle^{0.5}$ = 18 uK.Comment: 17 pages including 3 PostScript figures. Submitted to The Astrophysical Journal (Letters

Power Spectrum Estimators For Large CMB Datasets

Forthcoming high-resolution observations of the Cosmic Microwave Background (CMB) radiation will generate datasets many orders of magnitude larger than have been obtained to date. The size and complexity of such datasets presents a very serious challenge to analysing them with existing or anticipated computers. Here we present an investigation of the currently favored algorithm for obtaining the power spectrum from a sky-temperature map --- the quadratic estimator. We show that, whilst improving on direct evaluation of the likelihood function, current implementations still inherently scale as the equivalent of the cube of the number of pixels or worse, and demonstrate the critical importance of choosing the right implementation for a particular dataset.Comment: 8 pages LATEX, no figures, corrected misaligned columns in table