Integration of Geophysics And GIS
GIS and remote sensing
https://www.wur.nl/en/Education-Programmes/PhD-Programme/PhD-Vacancies/show/PhD-position-in-large-area-tropical-forest-biomass-estimation-and-uncertainty-assessments.htm?fbclid=IwAR3Hik6iMT8btsFIGxfDqRRyGttZvDpMgmrL9n0CpbaCH4EJDZzdqP-LF0s
If you are enrolling into PhD, then getting some complete theses is better than just a proposal.
You can explore image analysis of remotely sensed images.