The aim of the present beam-time request is to perform a direct measurement of the total muonium emission rate from silica aeeogel to vacuum including the region very close to the aerogel surface. Laser ionization of the thermal muonium is a good candidate for the ultraslow muon beam production needed for the muon g-2/EDM measurement as well as for special musr applications. We will use the relaxation of muonium spin precession as the measure of the muonium emission yield from several aerogel samples. The yield information is critical in choosing the target condition that gives the maximum muonium emission yield.