A fluid visualization and characterisation system comprising: a measuring section comprising a housing having a means defining a fluid flow path for fluid flow, the measuring section including: at least one transducer configured to generate and emit an ultrasonic signal into the fluid flow in the means defining the fluid flow path and arranged to be used in conjunction with a delay line element in contact with an outer wall of said means defining a fluid flow path in a non-invasive measurement configuration; and a receiver configured to receive reflections of the ultrasonic signal emitted by the at least one delay line transducer from reflectors in the fluid flow; a memory for storing data; and a processor operatively connected to the memory, the processor comprising: a velocity estimating module configured to apply one or more velocity estimation algorithms to received reflections of the ultrasonic signal, or data indicative thereof, to determine a velocity profile of fluid flow in the means defining the fluid flow path; a deconvolution module configured to apply a deconvolution algorithm at least to the determined velocity profile to determine a true velocity profile of the fluid flow in the means defining the fluid flow path; and a fluid visualization and characterisation module configured to determine characteristics of the fluid and/or fluid flow in the means defining the fluid flow path by using the determined velocity profile and/or the true velocity profile, characterised in that said at least one transducer is configured so that the focal point of the ultrasonic signal is located at a liquid-wall interface of the measurement section where the ultrasonic signal enters the fluid flow path, when in use. a measuring section comprising a housing having a means defining a fluid flow path for fluid flow, the measuring section including: at least one transducer configured to generate and emit an ultrasonic signal into the fluid flow in the means defining the fluid flow path and arranged to be used in conjunction with a delay line element in contact with an outer wall of said means defining a fluid flow path in a non-invasive measurement configuration; and a receiver configured to receive reflections of the ultrasonic signal emitted by the at least one delay line transducer from reflectors in the fluid flow; at least one transducer configured to generate and emit an ultrasonic signal into the fluid flow in the means defining the fluid flow path and arranged to be used in conjunction with a delay line element in contact with an outer wall of said means defining a fluid flow path in a non-invasive measurement configuration; and a receiver configured to receive reflections of the ultrasonic signal emitted by the at least one delay line transducer from reflectors in the fluid flow; a memory for storing data; and a processor operatively connected to the memory, the processor comprising: a velocity estimating module configured to apply one or more velocity estimation algorithms to received reflections of the ultrasonic signal, or data indicative thereof, to determine a velocity profile of fluid flow in the means defining the fluid flow path; a deconvolution module configured to apply a deconvolution algorithm at least to the determined velocity profile to determine a true velocity profile of the fluid flow in the means defining the fluid flow path; and a fluid visualization and characterisation module configured to determine characteristics of the fluid and/or fluid flow in the means defining the fluid flow path by using the determined velocity profile and/or the true velocity profile, a velocity estimating module configured to apply one or more velocity estimation algorithms to received reflections of the ultrasonic signal, or data indicative thereof, to determine a velocity profile of fluid flow in the means defining the fluid flow path; a deconvolution module configured to apply a deconvolution algorithm at least to the determined velocity profile to determine a true velocity profile of the fluid flow in the means defining the fluid flow path; and a fluid visualization and characterisation module configured to determine characteristics of the fluid and/or fluid flow in the means defining the fluid flow path by using the determined velocity profile and/or the true velocity profile,