The First Minister, while accepting there was "still a lot of work to do" to secure victory, said he "substantially changed" his style of campaigning after previous defeats in national elections.
Ahead of the SNP's victory in the 2007 Holyrood election he said he had decided to "accentuate the positive".
Mr Salmond told the BBC's Reporting Scotland: "I realised - and it took me a while in politics - that people want to vote 'for' something as opposed to 'against' something.
"Since then I think people would have to accept that the electoral results tend to vindicate that approach. And also they are vindicating the approach to this campaign because, since November, when we launched the White Paper, the average support in all opinion polls for 'Yes' has gone from 37% to 45%."
The pro-Union Better Together campaign has been accused by critics, and even by some supporters, of being too negative over North Sea oil and the currency, instead of pushing the Union's strengths.
It has prompted calls for a change in approach as polls narrow and independence campaigners have accused their rivals of being in disarray.
On Wednesday, a TNS poll showed that over half of 996 respondents, or 53%, said the Better Together campaign was negative while only 29% described the Yes campaign as such.
Mr Salmond said: "Gradually, month after month, we are gaining ground. We're not there yet, we have still got a lot of work to do, but the Yes campaign, because of our positive approach, which we are absolutely in thrall to, is gaining ground as we explain the arguments to the people of Scotland.
"It is really, really important as the Yes campaign moves forward, that we concentrate on issues which explain independence in terms of the progressive social change that can be brought about in Scottish society."