Cloud computing has become a popular solution for organizations implementing Earth Observation Systems (EOS). However, this produces a dependency on provider resources. Moreover, managing and executing tasks and data in these environments are challenges that commonly arise when building an EOS. This paper presents GeoNimbus, a serverless framework for composing and deploying spatio-temporal EOS on multiple infrastructures, e.g., on-premise resources and public or private clouds. This framework organizes EOS tasks as functions and automatically manages their deployment, invocation, scalability, and monitoring in the cloud. GeoNimbus framework enables organizations to reuse and share available functions to compose multiple EOS. We use this framework to implement EOS as a service for conducting a case study focused on measuring water resource changes in a lake in the south of Mexico. The experimental evaluation revealed the feasibility and efficiency of using GeoNimbus to build different earth observation studies.