  The Low Frequency Array (LOFAR) is the only existing radio interferometer
able to observe at ultra-low frequencies (<100 MHz) with high resolution (<15")
and high sensitivity (<1 mJy/beam). To exploit these capabilities, the LOFAR
Surveys Key Science Project is using the LOFAR Low Band Antenna (LBA) to carry
out a sensitive wide-area survey at 41-66 MHz named the LOFAR LBA Sky Survey
(LoLSS). LoLSS is covering the whole northern sky above declination 24 deg with
a resolution of 15" and a sensitivity of 1-2 mJy/beam (1 sigma) depending on
declination, field properties, and observing conditions. Here we present the
first data release. An automated pipeline was used to reduce the 95 fields
included in this data release. The data reduction procedures developed for this
project have general application and are currently being used to process LOFAR
LBA interferometric observations. Compared to the preliminary release,
direction-dependent errors have been corrected for during the calibration
process. This results in a typical sensitivity of 1.55 mJy/beam at the target
resolution of 15". The first data release of the LOFAR LBA Sky Survey covers
650 sqdeg in the HETDEX spring field. The resultant data products released to
the community include mosaic images (I and V Stokes) of the region, and a
catalogue of 42463 detected sources and related Gaussian components used to
describe sources' morphologies. Separate catalogues for 6 in-band frequencies
are also released. The first data release of LoLSS shows that, despite the
influences of the ionosphere, LOFAR can conduct large-scale surveys in the
frequency window 42-66 MHz with unprecedentedly high sensitivity and
resolution. The data can be used to derive unique information on the
low-frequency spectral properties of many thousands of sources with a wide
range of applications in extragalactic and galactic astronomy.
