The LOCOS project aims to use the Low Frequency Array (LOFAR) to measure the redshifted 21-cm signal from the epoch of cosmic dawn (40>z>15). Measuring the redshift evolution of the global (sky averaged) 21-cm signal from cosmic dawn is expected to cast light on the nature of the first stars and black-holes. In this talk, I will demonstrate a novel observational technique for such measurements that circumvents some of the challenges that are limiting existing single dipole experiments.
A single dipole experiment can measure the global 21-cm signal, but will require unprecedented calibration accuracy. Multi-element radio interferometers are highly calibratable, but being spatial differencing instruments, are insensitive to a global signal. However, by having the moon in their field-of-view, radio interferometers can measure the brightness contrast between the global signal and the moon. The moon behaves as a spectrally featureless blackbody at radio frequencies, thereby providing a stable temperature reference. In this talk, using LOFAR data, I will demonstrate this novel technique of interferometrically measuring a global signal.