2nd ESA CHRIS/Proba Workshop, ESRIN, Frascati April 28-30 2004

Field goniometer system for accompanying directional measurements Thomas Schneider

Limnologische Station der TU München

Proposals accepted by Chris/Proba scientific commitee: No. 48: BRDF estimation for surface types of the alpine environment with CHRIS/Proba multiangular data - A contribution for the improvement of atmospheric/topographic normalisation of data for monitoring the alpine environment ! forest, Oberammergau test site ! Proved that the degree of ambition was to high and postponed for the moment (too many variables due to extreme topography) No. 49: LAD estimation from CHRIS/Proba multiangle data calibrated with field spectroscopy derived BRDFs - a solution for the missing parameter in physical model inversion ? No. 50: Retrieval of bio-geo-physical parameter for vegetation canopy model inversion ! No. 49 and 50 put together as result of the 1th CHRIS/Proba workhop ! agriculture, super test site Gilching

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Data flow for the evaluation of RS data by the help of models as proposed by ESA AO /1-3381

Remote sensing data e.g.: σo, ρ

Ancillary information e.g.: sun illumination, rain, mean air temperature

Vegetation growth models e.g. : number of leaves, LAI

Direct models e.g.: σo, ρ Inversion algorithms

e.g.: biomass, crop yield under investigation

Geo- and biophysical parameters

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Trends of optical air or satellite borne systems: " resolution improvements (spatial, spectral, radiometric, temporal) " programmable systems with cross track pointing capabilities (Spot, Ikonos, Quick Bird, etc.) " “on-track” multiangle data registration (Spot 5, IRS 6, ALOS, HRSC, WAAC, DPA, LV, AirMISR, DMC, CHRIS/Proba, etc. " frame cameras (DMC), multispectral scanner, imaging spectrometer with unfavourable high to base line ratio (air borne: AVIRIS, MIVIS, Rosis, HyMap, ARES, etc.) Additional: " on the ground “real time” systems (HydroAgri, etc.) " etc.

! problem: illumination to observation geometries !

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General investigation concept:

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Specific goals : The creation of a calibration data base for the adaptation of physical models and their inversion for the surface type under the specific site conditions of the research area. !measurements appropriate for BRDF approximation !measurements covering the whole vegetation period !measurements documenting growth differences on subplots with differing field water storage capacities

Surface types under investigation: forests, crops, grassland, reed

Our requirements on such a device ?

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Basic requirements on the measurement device:

10 m

10°

“high, mobile and fast enough to achieve an acceptable amount of representative measurements for more than one surface during comparable illumination conditions” !representative plot section !high: 10m above target !mobile: movable within the plot !fast: one series within 20 min !max 10° aperture angle !more than one surface type

device concepts in use ? Limnologische Station der TU München

Step 1: check of existing solutions:

1. Goniometer principle (EGO, FIGOS) WAAC system [C] Spektroradiometer Parabola

[A]

2m Höhe

+75° -75° Steuerung [B]

Zielobjekt Weizenkiste

0°- 360°

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Evaluation of concepts: " FIGOS is the perfect system for physical measurements but : ! restricted mobility ! distance instrument / surface too short " Parabola very fast, measurement height sufficent but : ! only some few spectral bands, aperture too lrage (15) " WAAC very fast, narrow spectral bands, measurement height sufficient but: ! restricted on VIS/NIR

Conclusion ? ! no „ready made“ solution fulfilling our requirements!

Proceed to step 2: device development Limnologische Station der TU München

1th solution: Stable instrument position, changing view direction (PARABOLA; WAAC concept)

Assumptions:

Consequences

(i) Helmholtz reciprocity theorem is supposed to be valid

• arrangement is delivering measurements which are acceptable from the physical point of view

(ii) the backscatter characteristic right and left of the principal plane is symmetrical,

• measurements can be restricted on one part of the hemisphere (time saving assumption)

(iii) the plot as a whole is the object of interest:

• contradictory to the goniometer principle, not the observation position is changed but the measured section of the plot (simplify the measurement arrangement)

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The prototype …..

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Mobile Unit for Field Spectroradiometric Measurements (MUFSPEM) Developed in the frame of IKB Dürnast project Funded by DFG GER 3700

Moving head 0° -180° Azimuth - 80°- +80° Zenith

reference panel (Spectralon)

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MUFSPEM „half“ hemisphere measurement scheme:

Reference measurements „spectralon plate“ at the beginning and at the end of the series. Difference in time : 15-20 min Interpolation according to registration time of the measurement for reflectance calculation

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Change of position in accordance with the principal plane Hemispherical measurement set

Afternoon

Noon

N

Row alignment

Morning

High field capacity subplot

Low field capacity subplot

Aim: range of backscatter values within one plot over the day Limnologische Station der TU München

MUFSPEM interim results : • The Mobile Unit for Field Spectroscopy Measurements (MUFSPEM), MUFSPEM has been used over the period 1999 – 2001

•The concept for the measurement arrangement to be high, mobile and fast was reached • A data base for BRDF approximation throughout the vegetation period of winter wheat, winter barley and maize (74, 51 & 67 available BRDFhemispheres respectively) has been created. Rape not evaluated until now.

Some examples Limnologische Station der TU München

Wavelength dependency:

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Differences high and low capacity sites across the VP

20

60 30

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