Obrigado àqueles que comentaram e forneceram comentários dignos de resposta. Obrigado!
O que já existe hoje:
@Andy comentou :
For spacecraft splashdowns (certainly Gemini, maybe others) they used a green marker dye, but I don't know how long it lasted. That would be a good thing to start with as they must have tested how long the traces were visible when choosing it.
@RogerLipscombe comentou :
prestodye.com/sea-dye-markers says "30 to 40 minutes", depending on sea conditions. Apparently there's a standard: MIL-S-17980D.
E para os desafios:
@abelenky comentou :
Rough approximation: How many gallons of this stuff would you need for it to not dissipate in minutes? How much would that weigh? How often to airplanes crash in the sea? The cost and complexity just doesn't even come close to the benefit.