I was wondering why you accompanied this with a couple of party boys on the beach. It took me a minute to figure out that these are two people (hopefully both priests) celebrating the Eucharist.
We do "Mass in the Grass" ourselves once or twice a year. As a Scouter, I've attended outdoor services many a time. So I have no problem with this conceptually.
The issue is not that it is an improvised outdoor service, but rather that it seems hardly improvised at all. Look at the photo more closely. You will notice the symbolism of the trash can as well at the rainbow motif. In this case the rainbow does not symbolize a new covenant between God and man, but rather one between man and man or woman and woman.
Do you live in Florida? I have a friend here in Florida whose parish (very, very gay, btw) started doing "Mass on the Grass." Her kids have left the Church and, in fact, the Church is a joke in her town. Everybody knows it's nothing but gays and punch and cookies on the lawn.
There are norms in place that define how an outdoor Mass is to be conducted. There are also special kits for 'field masses'.
Twenty years ago, while visiting Assisi, I stumbled upon an 'open air' Mass. It was 'different', but the priest followed the established norms. No 'boogy board' altar. Reverence was pre-eminent.