Two academics at the London School of Economics are carrying out research into how the environment affects people's happiness. To help them gather the data for this research they have launched an iPhone app called mappiness.
If you download the app you will receive a notification between one and five times a day. The notification will ask you to open the app, briefly report how you're feeling and who you're with, where you are, and what you're doing. If you're outdoors and you're happy to, you'll be asked to take a photo of your surroundings as well.
You can also open the app and report on your feelings and situation, unprompted, as often as you like.
Anyone can keep an eye on the research being gathered by checking out the mappiness Google Map. The map shows the outdoor places where mappiness users have most recently reported feeling happy. If you click on an information window you can also view the photograph taken at that happy moment.
If charts and graphs are more your thing you can also check out the happiness meters and a graph of happiness levels charted over the past few days.