The Level 1 Specifications stipulate a sky coverage >95% with no gaps greater than 200 sq. deg.
The 2MASS scanning strategy was devised around 59,650 "Tiles" with dimensions of roughly 6° × 8.5´. Observations of these Tiles ensure coverage of the entire sky. Tiles were laid out such that adjacent ones would provide overlap of 10% (approximately 50´´) in right ascension and 8.5´ in declination. Three effects are responsible for decreasing the sky coverage from 100%:
|TABLE 1: Sky Coverage|
|Release Product||Area Missed||Sky Coverage||Notes|
|Atlas Images||0.706 sq.deg.||99.998%||Ten small gaps remain on the sky.|
|PSC||201.074 sq. deg.||99.513%|
|In addition to the missing coverage of 0.706 sq. deg. noted above, there are 46 effective gaps in RA and seven in Dec, where the overlap between adjacent scans falls below 20´´. The total area for these additional gaps is 1.258 sq. deg.|
|At H-band where the effect is worst, the total area "lost" to bright stars is 199.110 sq.deg.|
|XSC||<800 sq. deg.||>98%|
|In addition to the missing coverage of 0.706 sq. deg. noted above, there are 112 effective gaps in RA and 52 in Dec where the overlap between adjacent scans falls below 30´´. The total area for these additional gaps is 1.648 sq. deg.|
|The extended source processing also requires larger masking around bright stars than does the point source processing. In scans which lack very bright stars, the effective coverage for the XSC exceeds 98%.|
|Postage Stamps||<800 sq. deg.||>98%||The extended source postage stamps, since these are image cut-outs of sources detected by extended source processing, will have the same incompleteness as quoted for the XSC.|
The 2MASS All-Sky Release dataset far exceeds the Survey requirements for >95% sky coverage. As this missing area is scattered over the sky, all contiguous coverage gaps are well below the 200 sq. deg. upper limit as well.
[Last Updated: 2009 Nov 23; by J.D. Kirkpatrick]