Airport utility: Scan specific channels
I don't think the tool does what you wish. It treats scan as "check all channels" and may not even obey restrictions if you set them by hook or crook on which channels are allowed on the interface. It allows you to pre-filter by SSID name as opposed to channel:

airport --scan=whatever


For sniffing, you can use the Wireless Diagnostics application, but it's not command line based/enabled as far as I can tell.



Once you start the program, look in the Window menu for the options available on your OS (the tool is improving over time IMO with more features and capabilities).

You are right and the authors of the airport manual page agree that "airport more information needed here"