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Observations of winds in mesospheric airglow layers have been made at Mt. John (44°S,170°E), New Zealand for some years. We present a modelling study of airglow emissions which shows that the properties of wind detection based on airglow emission means that high-frequency gravity waves are effectively filtered from the wind spectrum observed. This filtering means that any waves with periods of the order of hours should be detectable in the record (as they will not be hidden in the noise of the higher-frequency waves ubiquitous at these heights). One example of such a wave is shown. As part of the analysis, we show that because the airglow layers differ in width, some waves might be observed in only one airglow layer, even when present in both. [Copyright &y& Elsevier]