The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio survey that covers the whole sky north of 30{deg} at a wavelength of 92cm (330MHz) to a limiting flux density of approximately 18 mJy (5{sigma}). This survey has a resolution of 54"x54" cosec(delta) and a positional accuracy for strong sources of 1.5". The WENSS project is a collaboration between the Netherlands Foundation for Research in Astronomy (NFRA/ASTRON) and the Leiden Observatory. Introduction to the WENSS: The Westerbork Northern Sky Survey (WENSS) is a radio survey made with the WSRT at wavelengths 92 and 49 cm. At 92 cm the entire sky above declination 30{deg} is covered. The other wavelength regime does not cover the whole sky, but only 30-50 percent, due to the amount of telescope time that is needed to do this. Using a synthesis array like the WSRT means that we get a better resolution than single dish observations, but also has the disadvantage of a smaller field of view, unless we find a way of dealing with wide field imaging. The solution for this problem is mosaicing. Instead of making one observation of a large field we make a lot of snapshots of different fields and bind them together with the help of special build software. A typical mosaic contains 80 pointing centres. Each pointing centre is sampled during 20 seconds and then the telescope moves to another centre. This takes about 10 seconds. After 40 minutes all fields are scanned and the procedure starts again. This means that in a 12 hour observation each field is scanned 18 times. To move grating rings of the map 6 different baseline settings are used, so 1 mosaic data block involves 72 hours of observational data. Each pointing centre is located at half half-power maximum beamwidth in order to get a smooth sampling grid of the data. The noise background is uniform up to 5 percent. At 92 cm (declination 30{deg}) a mosaic block is about 10 by 14{deg} large. The final product that the WENSS survey produces contain 6x6{deg} frames taken from the mosaic blocks. They are centered on the new POSS plate positions (5{deg} grid). The limiting flux density will be about 15 mJy (5 sigma) at both wavelengths. As a result the final catalogue will consist of 300,000 sources at 92 cm and 60,000 at 49 cm. The positional accuracy will be superior to all other all sky surveys (5" for the faint sources to better than 1" for the stronger sources). A large number of sources will have sufficient accurate positions to allow optical identification using a digitized version of the Palomar Sky Survey made with the APM at Cambridge. Final maps will be made at different resolutions in order to make accurate spectral index measurements. At each wavelength we will make high, medium and low resolution maps (1', 2.5' and 4' resolution at 92 cm and 0.5', 1' and 2.5' resolution at 49 cm). Maps will be made with all Stokes parameters (I, Q, U and V). This means that source information will be available both on spectral type and polarization characteristics. This is important for using the catalogue as a database for finding sources based on well known selection criteria, such as steep spectra for high redshift radio galaxies.

Cone search capability for table VIII/62/wenss (Combined table from original tables)