SARAS is a correlation spectrometer connected to a frequency independent antenna that is purpose-designed for precision measurements of the radio background at long wavelengths .
The design , calibration and observing strategies admit solutions for the internal additive contributions to the radiometer response , and hence a separation of these contaminants from the antenna temperature .
We present here a wideband measurement of the radio sky spectrum by SARAS that provides an accurate measurement of the absolute brightness and spectral index between 110 and 175 MHz .
Accuracy in the measurement of absolute sky brightness is limited by systematic errors of magnitude 1.2 % ; errors in calibration and in the joint estimation of sky and system model parameters are relatively smaller .
We use this wide-angle measurement of the sky brightness using the precision wide-band dipole antenna to provide an improved absolute calibration for the 150-MHz all-sky map of Landecker & Wielebinski ( 7 ) : subtracting an offset of 21.4 K and scaling by factor 1.05 will reduce the overall offset error to 8 K ( from 50 K ) and scale error to 0.8 % ( from 5 % ) .
The SARAS measurement of the temperature spectral index is in the range -2.3 – -2.45 in the 110-175 MHz band and indicates that the region towards the Galactic bulge has a relatively flatter index .