Cold and Arid Regions Environmental and Engineering Research Institute, CAS

Measurement of Water Cycle

Xin Li 李 新

3.2 Soil moisture

Observations of soil moisture from the ground to the space

Heye et al., 2009

• Direct method– Gravimetric method

• Indirect– Tensiometric (energy status – related to moisture)

• Tensiometers• Resistance blocks• Psycrometer…

– Volumetric• Nuclear method (Neutron probe)• Dielectric methods

– Time Domain Reflectometry (TDR)– Frequency Domain Reflectometry (FDR)– Capacitance, TDT, ADR, Phase Transmission

• Other

Measurement method of Soil moisture

TDT

FDR

TDR

by Rui Jin

COSMOS— COsmic-ray Soil Moisture Observing System

Space:Incoming high-energy cosmic-ray proton

Atmosphere:Generation of secondary cosmic rays

Ground:Slowing down thermalizationand absorption

Cosmic Ray measures the 12 cm~76 cm soil moisture in a 600 m radius The data can be obtained in hourly step

by Rui Jin

Hi-WATER

Wireless sensor network

communication：IPV6, GPRS, Radio, 2.4G observation: soil temperature, soil moisture, soil conductivity,

dielectric constant, air temperature/humidity, wind speed/direction, LST, snow depth and precipitation

solar panel + storage battery

WATERNET

Sensor Spatial resolution

Temporal resolution Accuracy example

radiometer 25-50km daily high AMSR-E、SMOS

scatterometer 25-50km daily moderate ASCAT

SAR 30m~1000m Tens of days moderate ASAR、RADARSAT-2

optical 1000m daily moderate MODIS、ASTER

SMAP: Soil Moisture Active & PassiveLaunch in 2015，3~40km，~3 days，L-band

use L-band combine the passive and active microwave fuse the NIR-TIR observation

SMOS: Soil Moisture and Ocean SalinityLaunch in 2009，40km，~3 days，L-band

Tb(-)Tb(+)=(1-Γ)*Tb(-)

Surface Scattering

Volume Scattering

Tb(-)Tb(+)=(1-Γ)*Tb(-)

Surface Scattering

Volume Scattering

Very Dry Condition

Tb(-)Tb(+)=(1-Γ)*Tb(-)

Surface Scattering

Volume Scattering

Wet Condition

Soil Moisutre

Em

issi

vity

May 01-10 May11-20 May 21-31 Jun 01-10 Jun 01-10

Jun 21-30 Jul1 01-20 Jul 11-21 Jul 21-31 Aug 01-10

Aug 11-20 Aug 21-31 Sep 01-10 Sep 11-20 Sep 21-30

Soil moisture: GAME-Tibet meso-scale experiment May-October 199810 day composite

0.0

VWC

y = 0.9636x - 0.05

0.00

0.10

0.20

0.30

0.40

0.50

0.00 0.10 0.20 0.30 0.40 0.50Mv (Obs. at 4cm depth)

Mv

(LU

T)

0.5

0.4

0.3

0.2

0.1

0.0

Detect soil freeze/thaw from passive microwave remote sensing

Start date of soil freeze

Soil freeze/thaw data set derivedfrom PM remote sensing

Frozen days (2002/10/01-2003/09/30)

FreezeThawDesertPrecipitationJin et al., 2009

SMAP mission

45

3.3 Evapotranspiration

ET measurement

methods

Liquid water consumption

Water vapor transmission

Water balance method

Plant physiological method, such asTDP(Thermal dissipation sap flow velocity probe)

Eddy covariance system

Bowen ratio-energy balance method

Air dynamics method

Resistance method

Scintillometer

Field water balance method

Zero flux plane method

Evaporation pan, evaporation pool

Lysimeter

Evaporator

Ground measurements

by Prof. Shaomin Liu

Lysimeter

Sketch map of lysimeter

P: precipitation; I: irrigation; Pa: infiltration recharge; Eg: consumptionof groundwater; Δw：the change in water storage。

Measuring ET, groundwater evaporation consumption, infiltration, etc.

by Prof. Shaomin Liu

Weighting lysimeterThe surface area of Lysimeter isusually 1-5 m2, 1-2 m depth, withthe accuracy of 0.02 mm (weighting34 tons) and resolution of 60 g. Themeasuring period is less than 1 h.

Representative？Environmental factors？

by Prof. Shaomin Liu

Graswang

ΔTem

p ~ 0.6 °C

ΔN

S ~ 70 mm

ΔTem

p ~ 2.5 °C

ΔN

S ~ 480 mm

Bad Lauchstädt

Sauerbach

Schäfertal

Rottenbuch

Fendt

Wüstebach

Rollesbroich

Sehlhausen

Lysimeter-Network TERENO SoilCan

ΔTem

p ~ 3.7 °C

ΔTem

p ~ 3.0 °C

ΔN

S ~ 160 mm

ΔN

S ~ 880 mm

Demmin

Dedelow

Scheyern

From Harry Vereechen

EC is a fast response instrument, and can measure of verticaland horizontal velocity components, temperature, water vapor,carbon dioxide directly. The sampling frequency is usually at 10-20 Hz with the average period of 30 min, which can capture themain turbulent eddies contributions. The flux (H, LE, carbondioxide) can be obtained by calculation of the covariance ofvertical velocity and related scalars.

Eddy Covariance system(EC)

-4

-2

0

2

4

6

8

10

Umean (m/s)

CO2 (100g/m3)

H2O (g/m3)

T (°C)

W (m/s)

Raw data measured by eddy covariance system (Tongyu station: 10:00－10:05 on 20 Oct., 2002) by Prof. Shaomin Liu

The turbulent fluxes can be obtained from the calculation of the covariance between vertical velocity and related scalars.

ρ : air density; w’: vertical velocity fluctuation, C’: related scalarfluctuation.

A series basic assumptions behind:(1) Stationary turbulence;(2) Horizontal homogeneity(advection not included);(3) Constant flux layer exists;(4) Eddies at all scales are sensed；(5) Sensed flux is representative of the underlying surface.

However, the assumptions cannot meet in the reality. Thus,there will be large errors if necessary corrections are not applied .

[Swinbank, 1951]

Eddy covariance system

Energy imbalance？The energy cannot be captured from larger eddies and secondary circulations contributions.

Limitations in LAS (scintillometer) observation: meteorological limitations in long term operations (precipitation, poor visibility, weak turbulence, etc) and methodological limitations (signal saturation, inner-scale dependence of the signal, and tower vibrations).

3.4 Snow

Snowfall

Original photo, US Weather Bureau, 1917 in “Boy with Weather Men” p. 224

A batch of snow gauges at NCAR's Marshall Field Site—includes an example of the world's accepted standard for snow-gauge shielding, the Double Fence IntercomparisonReference (foreground). (Image courtesy Roy Rasmussen, NCAR.)

The T-200 precipitation gauge with unconstrained-baffle alter shield, located in Binggouwatershed, China

Snow water equivalentContactless measurementContact measurement

GMON observation

Ground based microwave observation

Snow pillow

Contact measurement: destroyed underlying conditionlow accuracy for shallow snowpackinfluenced by wind

Contactless measurement: original underlying conditionfine accuracy for most snowpacknot influenced by wind and other factors by Hongyi Li

Snow density and water content Snowfork

SPA, snow pack analyzer

Snow consists out of ice,water and air. Measuringthe complex dielectricitywith at least twofrequencies allows toestimate the volumecontents of the individualcomponent.

by Hongyi Li

Synthesis snow observation