Can the reionization epoch be detected as a global signature in the cosmic background

The reionization of the Universe is expected to have left a signal in the form of a sharp step in the spectrum of the sky. If reicnization took place at 5 less than or similar to z(ion) less than or similar to 20, a feature should be present in the radio sky at 70 less than or similar to v less than or similar to 240 MHz due to redshifted H I 21-cm line emission, accompanied by another feature in the optical/near-IR at 0.7 less than or similar to lambda less than or similar to 2.6 mu m due to hydrogen recombination radiation. The expected amplitude is well above fundamental detection limits, and the sharpness of the feature may make it distinguishable from variations due to galactic anti extragalactic foregrounds. Because this is essentially a continuum measurement of a signal which occurs over the whole sky, relatively small telescopes may suffice for detection in the radio. In the optical/near-IR, a space telescope is needed with the lowest possible background conditions, since the experiment will be severely background-limited.