BRDFs acquired by directional radiative

measurements during EAGLE and AGRISAR

Joris Timmermans, Christiaan van der Tol, Kitsiri Weligepolage,

Zoltan Vekerdy, Li Jia & Bob Su

Problem

Multidirectional measurements are relevant, but scarse–Separate vegetation-soil components– Inversely derive surface characteristics–Test radiative transfer models

Objective

To acquire optical and “thermal”BRDFs for comparison with 3D Radiative Transfer models–SAIL

•+ Fast•homogeneous

–DART•- slow•heterogeneous

Comparison requirements

• Input of models:–Sun angles– Incoming radiation–Component temperatures–Vegetation structure

• LDF, LAI• Height/width individual plant

• Output–Optical and Thermal BRDF

Methodology: Optical and Thermal BRDF

• Goniometer– Mechanical Machine– Two freedom of motion

• The first degree of freedom: azimuth angles, θ.

• The second degree of freedom: zenith angles, φ

• Sensors– Canon Digital Camera – Irisys Thermal Camera– Everest Temperature Radiometer– GER Spectrometer– CIMEL Radiometer

Sensors

Single pixel Image

• Optical

• Thermal

Methodology:Goniometric-measurements

• Max. angles per measurement = 15• More angles => more transects

• Pointing from Tower– Wooden frame– 4 directions

• North, South, East, West

• Changing field of measurement– Size of area– species

Methodology: directional tower-measurements

Overview: Field Measurements

• EAGLE2006– 06-27 June– Two sites

• Cabauw Tower• Speulderbos Tower

• AGRISAR2006– 02- 07 July 2006– Single Site

• Gormin

Field Radiative Measurements

Vegetation Site Optical Thermal

Forest E ASD -

Pine tree E ASD -

E

E

A

A

A

A

Grass GER Irisys, Everest

Young Corn GER Irisys, Everest

Mature Corn ASD Irisys

Wheat ASD Irisys, Everest, CIMEL

Sugar beat ASD Irisys, Everest, CIMEL

Barley ASD Irisys, Everest

ASD: Measurements

• BRDFs obtained– Radiance

• Splice corrected– Radiance ->Reflectance

• White reference Panel

– Quality check• Multiple reflectances

• Spectrum – >1700nm contains a lot of noise

• Splice correction

ASD: Reflectance Ratio

• Normalized Reflection Ratio– (Rθ-Rn)/(Rθ+Rn)

• Divide into three parts– VIS [400-740nm]– NIR [800-1000nm]– MNIR[1500-1700nm]

ASD: Investigation results

• max(std(Ř)) Strong Directionality– VIS

• Wheat• Sugar beat• Grass

– NIR• Maize (young)• Maize (mature)

– MNIR• Wheat• Sugar beat• Grass

Vegetation VIS NIR MWIR

9.18 14.53

09.54

16.56

11.58

08.00

17.28

16.73

-

9.17

20.98

13.63

15.39

25.59

24.12

Forest

-

10.79

09.22

09.76

12.29

18.38

7.54

11.87

-

Pine tree

Grass (tall)

Young Corn

Mature Corn

Wheat

Sugar beat

Barley

Everest: measurements

• Barley

• Maize(young)

Everest: Investigation results

• Max (STD /Mean)*1000– Strong Directionality

• Young Maize• Wheat

Vegetation TIR: Everest

Forest -

Pine tree -

97.0

179.0

-

116.6

66.0

20.5

Grass

Young Corn

Mature Corn

Wheat

Sugar beat

Barley

Irisys measurements

• Wheat

• Maize (Mature)

-60 -30 N 30 60

θ = 0

θ = 90

-60 -30 N 30 60

θ = 0

θ = 90

Irisys: Temperatures profile

• Temperature profile–Wheat

• Mean: Ť• Std: T’

–Maize (Mature)• Mean: Ť• Std: T’

Irisys investigation results1

• max (std(Ť)/mean(Ť))*1000• for different angles

– Strong Directionality• Young Corn• Mature Corn

– Weak Directionality• Barley• Wheat

– Component temperature extraction• Strong Directionality

Vegetation TIR: Irisys

Forest -

Pine tree -

48.7

69.6

67.9

56.4

46.69

20.7

Grass

Young Corn

Mature Corn

Wheat

Sugar beat

Barley

Irisys investigation results2

• Std(T’)/Mean(T’) for different angles– Strong Separation potential

• Young Corn• Mature Corn

– Weak Separation potential• Barley• Wheat

– Component temperature extraction• Strong Directionality

Vegetation TIR: Irisys

Forest -

Pine tree -

04.17

09.30

12.47

02.29

07.15

01.59

Grass

Young Corn

Mature Corn

Wheat

Sugar beat

Barley

CIMEL measurements

• Barley

CIMEL measurements

• Sugar beat

CIMEL

• Max(STD/MEAN)*1000– Strong Directionality

• Barley

• No Eagle measurement– CIMEL malfunction

Vegetation B1 B2 B3 B4 B5

15.5

B6

Sugar beat 20.8

38.437.4

15.0

36.3

18.7 22.714.7

32.0 40.9 36.4Barley

Conclusion

• BRDFs obtained–Optical

• High directionality of Wheat and Grass in VIS and MNIR

• High directionality of Maize (Y/M) in NIR

–Thermal• High directionality of Wheat and Maize and

Sugar beat.• High potential of component separation in

Irisys Maize (Y/M) measurements

Future work

• Implement component separation. • Compare measured BRDFs with

SAIL/DART derived BRDFs

Acknowledgements

• Jena University • Valencia University• SRON and ESA