In GreenOrbs application of canopy closure estimates, we mainly address the following design issues: 

1. Generic estimation model. 
    We design a generic estimation model that works for non-vertical irradiations of sunlight and various vegetation species.

2. Sensor motes encapsulation and installation 
    We design and produce firm weatherproof sensor motes that are sustainable for very long time in the wild environments.

3. Processing of uncertain sensory data. 
    The sensor readings are often error-prone due to the complex deployment environment and diverse instrumental errors, which may lead to inaccurate      measurements.

4. Distributed cooperative node state monitoring. 
    A distributed cooperative mechanism is designed for sensors to accurately judge their statuses in a distributed manner so as to save computation and transmission cost.

From a macroscopic view, GreenOrbs is facing more research challenges towards a long-term kilo-scale WSN.

1. Light-weight network diagnosis and management

2. Online fault detection, tolerance, and correction

3. Synchronization and scheduling

4. Hardware and software reliability

5. Data collection in large-scale low duty-cycle WSNs