"an essential means" is a correct phrase that can be used in written English.
You could use it to describe something that is necessary to achieve a certain goal or effect. For example, "Having a support network of friends is an essential means of maintaining mental health."
For Mumbaikars trains are an essential means of transport.
As Alan Johnson, a former home secretary, pointed out, biometrics were an essential means of identification.
Vision screening is an essential means of identifying children at risk of developing amblyopia.
The power to pardon is an essential means of justice, allowing a governor to right what the law got wrong.
Similar to the validation of image segmentation techniques, distance metrics are an essential means to validate model-based visualization techniques.
Nowadays, society has increasingly relied on convergent networks as an essential means for individuals, businesses, and governments.
Mapping provides an essential means of visualizing the complexity of the published data and identifying geographical trends and processes.
Making matters worse, the Taliban have issued a new decree threatening death to any relief worker caught using a satellite telephone, an essential means of communication.
Numerical modelling studies are an essential means of assessing hydrological and geomorphological impacts of changing rainfall patterns resulting from climate variability.
Sediment source fingerprinting provides an essential means for estimating sediment source contributions, which are needed not only for soil conservation planning but also for erosion model evaluation/refinement.
In an environment of globalisation, intense competition and rising R&D costs, collaboration has become an essential means of sustaining technological growth.
