NSCPHD1153 Cosmic-ray hydrometrology: measuring water at the land surface using cosmic-ray neutrons

Cosmic-ray method

Cosmic-ray neutrons can be used to measure water at and near the land surface, mainly soil water, snow and water in and on vegetation. The cosmic-ray method takes advantage of the inverse relation between the intensity of cosmogenic neutrons in air above land surface and soil moisture. With a unique horizontal footprint of hectometers and a vertical footprint of decimeters, cosmic-ray measurements average out small-scale variations in soil moisture and provide an area-average, representative measure of soil moisture. The cosmic-ray method has been adopted widely and many new applications are being developed. Examples include measuring snow water equivalent and vegetation water equivalent, determining infiltration rates and unsaturated hydraulic conductivity of soils, mapping soil moisture over large areas using mobile cosmic-ray probes, measuring rainfall rates, and measuring the amount of snow and liquid water on canopy.

Course scope

In the course we will discuss the principles and applications of the cosmic-ray method for measuring water at the land surface. The course will consist of lectures, individual work assignments (reading papers and conducting computations), and discussion sessions. The students will learn about all aspects of the cosmic-ray method, including the basic cosmic-ray physics (why the method works), data collection (the instrument and infrastructure), calibration, and data processing and interpretation (how the method works). We will also discuss how the cosmic-ray data can be used together with other data to provide better products, and how the cosmic-ray measurements can be used within hydrological framework for example to understand mass balance.

Course outline

Day 1, morning: surface moisture

Introduction to and overview of the course

Importance of surface moisture

Soil moisture in hydrologic cycle

Spatial heterogeneity of soil moisture

Methods for measuring soil moisture at different scales

Other reservoirs of water at the land surface

Summary, questions and discussions.

Day 1, afternoon: cosmic rays on Earth

Elements of nuclear physics

Basic definitions

Principles of cosmic-ray physics

Spatio-temporal variations of cosmic-ray neutrons

Hands-on:

- basic/useful computations/algorithms;

- acquiring and manipulating data sets;

Summary, questions and discussions.

Work assignments.

Day 1, evening:

Work assignments (reading, computations, analysis)

Day 2, morning: measuring soil moisture with cosmic-ray neutrons

[Optional: reports from assigned work]

Cosmic-ray method for measuring surface moisture

Principles

Response function

Ancillary data needed

Computations (including corrections)

Calibration

Support volume (2D footprint, soil thickness, volume of air)

Summary, questions and discussions.

Day 2, afternoon: measuring other water at the land surface

Snow water equivalent

Water in vegetation

Intercepted water (rain, snow)

Hands-on:

- full computation - from neutron intensity to soil moisture;

- computing effects of individual variables (e.g., pressure, humidity);

- computing effects of lattice water and organic matter;

Summary, questions and discussions.

Work assignments.

Day 3, morning:

Methods for measuring cosmic-ray neutrons

High energy vs low energy

Neutron monitor

Neutron detectors – thermal, epithermal, fast

Instrument design for cosmic-ray method

Data acquisition, transmission, processing and dissemination

Data levels

COSMOS and similar networks

Cosmic-ray method

Cosmic-ray neutrons can be used to measure water at and near the land surface, mainly soil water, snow and water in and on vegetation. The cosmic-ray method takes advantage of the inverse relation between the intensity of cosmogenic neutrons in air above land surface and soil moisture. With a unique horizontal footprint of hectometers and a vertical footprint of decimeters, cosmic-ray measurements average out small-scale variations in soil moisture and provide an area-average, representative measure of soil moisture. The cosmic-ray method has been adopted widely and many new applications are being developed. Examples include measuring snow water equivalent and vegetation water equivalent, determining infiltration rates and unsaturated hydraulic conductivity of soils, mapping soil moisture over large areas using mobile cosmic-ray probes, measuring rainfall rates, and measuring the amount of snow and liquid water on canopy.

Course scope

In the course we will discuss the principles and applications of the cosmic-ray method for measuring water at the land surface. The course will consist of lectures, individual work assignments (reading papers and conducting computations), and discussion sessions. The students will learn about all aspects of the cosmic-ray method, including the basic cosmic-ray physics (why the method works), data collection (the instrument and infrastructure), calibration, and data processing and interpretation (how the method works). We will also discuss how the cosmic-ray data can be used together with other data to provide better products, and how the cosmic-ray measurements can be used within hydrological framework for example to understand mass balance.

Course outline

Day 1, morning: surface moisture

Introduction to and overview of the course

Importance of surface moisture

Soil moisture in hydrologic cycle

Spatial heterogeneity of soil moisture

Methods for measuring soil moisture at different scales

Other reservoirs of water at the land surface

Summary, questions and discussions.

Day 1, afternoon: cosmic rays on Earth

Elements of nuclear physics

Basic definitions

Principles of cosmic-ray physics

Spatio-temporal variations of cosmic-ray neutrons

Hands-on:

- basic/useful computations/algorithms;

- acquiring and manipulating data sets;

Summary, questions and discussions.

Work assignments.

Day 1, evening:

Work assignments (reading, computations, analysis)

Day 2, morning: measuring soil moisture with cosmic-ray neutrons

[Optional: reports from assigned work]

Cosmic-ray method for measuring surface moisture

Principles

Response function

Ancillary data needed

Computations (including corrections)

Calibration

Support volume (2D footprint, soil thickness, volume of air)

Summary, questions and discussions.

Day 2, afternoon: measuring other water at the land surface

Snow water equivalent

Water in vegetation

Intercepted water (rain, snow)

Hands-on:

- full computation - from neutron intensity to soil moisture;

- computing effects of individual variables (e.g., pressure, humidity);

- computing effects of lattice water and organic matter;

Summary, questions and discussions.

Work assignments.

Day 3, morning:

Methods for measuring cosmic-ray neutrons

High energy vs low energy

Neutron monitor

Neutron detectors – thermal, epithermal, fast

Instrument design for cosmic-ray method

Data acquisition, transmission, processing and dissemination

Data levels

COSMOS and similar networks