The ratio of emission intensities of the second positive N2(C3Πu, v′ = 0) → N2(B3Πg, v = 0), 337.1 nm and first negative (B → (X, 391.4 nm systems of nitrogen have been measured in a nanosecond surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 1-3 bar for different polarities of the high-voltage (HV) pulse. For all the investigated conditions, the ratio of emission intensities at the wavelengthes 391.4 and 337.1 nm, measured experimentally, is systematically higher for the positive polarity of HV electrodes. To analyze the spatial distribution of N2(C3Πu) and (B emissions, comprehensive two-dimensional numerical modeling for P = 1 bar has been performed. The details of the formation of a narrow gap between the dielectric surface and the streamer channel in the case of positive polarity of HV electrodes are discussed. The ratio of integrated over space calculated emission intensities, , has been analyzed and compared with obtained experimental data. A good agreement was obtained for a negative polarity SDBD. For a positive polarity discharge, for all the considered conditions. Explanation for the observed effect is suggested.