The in-flight calibration system for the airborne imager GLORIA

Transcription

1 CALCON Technical Conference Utah State University, Logan, UT, USA August 4, 04 F. Olschewski, A. Ebersoldt, F. Friedl-Vallon, B. Gutschwager 4, J. Hollandt 4, A. Kleinert, C. Piesch, C. Monte 4, P. Preusse 3, J. Ungermann 3, R. Koppmann The in-flight calibration system for the airborne imager GLORIA University of Wuppertal, Wuppertal, Germany Karlsruhe Institute of Technology, Karlsruhe, Germany 3 Research Center Juelich, Juelich, Germany 4 Physikalisch-Technische Bundesanstalt, Berlin, Germany

2 Outline The in-flight calibration system for the airborne imager GLORIA The Airborne Instrument GLORIA Calibration Concept and Requirements Design of the GLORIA BlackBodies Emissivity, Uniformity and Uncertainty Performance of the GLORIA BlackBodies Suggestions for Improvement Summary and Conclusion

3 GLORIA Gimballed Limb Observer for Radiance Imaging of the Atmosphere photo: Falcon, DLR Joint project of Research Center Juelich and Karlsruhe Institute of Technology, Germany Airborne Imaging Michelson Fourier Transform Spectrometer (7 3 μm) GLORIA provides detailed images of the upper troposphere/lower stratosphere (UTLS) region To study small-scale atmospheric dynamics (e.g. Stratosphere-Troposphere Exchange) Measurements of atmospheric temperature fields, cloud parameters, aerosols, water vapor, ozone, and about ten other trace species 3

4 GLORIA deployed on board different airborne research platforms HALO photo: KIT photo: KIT GLORIA inside the belly pod of HALO M55-Geophysica with GLORIA, 0 4

5 GLORIA A unique tomographical measurement scheme pointing of line-of-sight at azimuth angles from 45 to 35 The Gimbal Concept of GLORIA 5

6 GLORIA Imaging Michelson Fourier Transform Spectrometer spectral range: cm - (Wavelength: ~ 7 3 μm) spectral resolution:.5 cm - (dynamics mode) 0. cm - (chemistry mode) two-lens aspherical telescope beam diameter: ~ 36 mm FOV: 4.07 x 4.07 altitude range: from ~ 4 km to flight level Michelson Interferometer D MCT detector array 8 x 8 pixels 6384 interferograms in less than 0 sec 6

7 GLORIA Calibration concept If the detector is linear, a two-point calibration is sufficient for gain and offset determination. The method of choice: Two high emissivity two well-defined temperatures. L a S a Bh Bc Sh Sc gain Bh B c Sc Bc Sh S c offset with: L: spectral radiance a: atmospheric S: measured detector signal h: hot blackbody B: spectral blackbody radiance (Planck function) c: cold blackbody 7

8 GLORIA Calibration requirements Two point calibration with 0 K below ambient temperature and 30 K above ambient temperature, respectively Two identical high-precision blackbodies, independently stabilized at two different temperatures Large optical surface: 6 mm x 6 mm GLORIA In-flight Calibration System Thermal uniformity: < 0.5 K Emissivity: > Temperature uncertainty: < 0. K Temperature stability: < 0.05 K/min Overall calibration uncertainty: < % 8

9 GLORIA BlackBody Design GLORIA- Schwarzkörper von Christian Rolf Optical surface: Array of 49 single pyramids (7 x 7) coated with NEXTEL-Velvet Coating 8-9

10 GLORIA BlackBody Design Thermal protection through polystyrene foam sheets Concept of the GLORIA BlackBody (GBB) 0

11 GLORIA BlackBody Design GBB Operation without cold trap

12 Geometry factor calculation according to John R. Howell 0. : For A 4 tan 4 tan 4 4 tan 4 tan 4 ln AB F X Y Y X X X X Y X X Y Y Y Y X Y B A A F Computed effective emissivity: NEXTEL-Velvet Coating 8- has a measured emissivity of greater in the spectral range between 5 µm and µm (Lohrengel, PTB, 996) Effective emissivity GLORIA BlackBody

13 GLORIA BlackBody Spectral variation of relative emissivity Results of PTB measurements 3 no significant deviation from no local effects no spectral features 3

14 GLORIA BlackBody European Metrology Research Programme: ITS-90 traceability PTB GBBs were calibrated inside the Reduced Background Calibration Facility (RBCF) of PTB Radiation temperature 00 hpa between -50 C and 0 C The broadband radiation thermometer VIRST (8 µm - 4 µm) was used. Direct comparison of the GBBs with reference cavity blackbody radiator VLTBB Directly linked to the primary national SI standards of radiation temperature in Germany The resistance value of each PRT is directly related to the radiation temperature at PRT position Measurements of spectral radiance via a Fourier Transform Spectrometer 4

15 GLORIA BlackBody Thermal uniformity of optical surface t S / K Infrared image of the 008 prototype taken in the lab (ambient T and p): Achieved thermal uniformity: ~ 80 T GBB = 78 K GBB-H radiation temperature measured by RBCF (PTB) (T GBB = 33 K) The temperature gradient between the pyramid apex and the base is less than 40 mk for GBB-C at 43 K and less than 0 mk for GBB-H at 73 K. 5

16 GLORIA BlackBody Short-term and long-term stability (a) Short-term stability: 0.6 mk/min (b) Long-term stability (0 / 03) 6

17 GLORIA BlackBody GLORIA calibration uncertainty Radiance uncertainty as a function of wavenumber (T BBC = 30 K, T BBH = 70 K) 7

18 GLORIA BlackBody GLORIA calibration uncertainty Radiance uncertainty as a function of GBB-C and GBB-H temperatures 8

19 Temperature [K] GBB Inflight Performance EssenCe Geophysica Flight # (Kiruna, Sweden, Dec 6, 0) Achieved performance Uniformity: +/- 50 mk time [UTC] Performance of GBB-H optical surface during flight Noise: T drift: +/- 5 mk < 5 mk / 30 min 9

20 GBB Inflight Performance TACTS CAMPAIGN: HALO Flight #0 (6.09.0) Time [UTC] Event GBB-C (T_S00) GBB-H (T_S00) 5:5 Cooling begins :00 HALO Takeoff T_S00 T_amb 7:07 T_S00 < T_amb -0K , 7:39 T_S00 < T_amb -5K 68 44,5 5 8:55 T_S00 < 40 K : deltat_max ,5 3:6 T_S00_min ,9 5: End of (active) cooling :38 HALO final descent :55 HALO landing

21 GBB Performance Performance vs. Requirements Requirement Performance Temperature (GBB-C) T(amb) 0 K T(amb) 0 K Temperature (GBB-H) T(amb) + 30 K T(amb) + 30 K Temperature uncertainty < 0. K ~ 0.05 K Emissivity > Thermal uniformity < 50 mk < 0 mk Temperature stability < 5 mk/min 0.6 mk/min Calibration uncertainty < % < 0.3 %

22 GLORIA ESMVAL Flight on SEP 3, 0 (Cape Town Cape Town) Kapstadt Cape Town J. Ungermann, FZJ

23 GLORIA 3D Retrieval Result J. Ungermann, FZJ 3

24 GLORIA BlackBody Suggestions for improvement Smaller spatial temperature inhomogeneity by a modified temperature control software Improvement of power management in order to operate GBB-C at a lower temperature Reduction of thermal mass by a new design of the pyramid array with an increased number of significantly smaller pyramids In future designs removable thermally treated/aged PTR sensors, which are calibrated as contact thermometers at a 30 mk uncertainty level, shall be used. 4

25 Summary and Conclusion The in-flight calibration system for the airborne imager GLORIA GLORIA is an airborne imager designed for tomographic measurements in the upper troposphere / lower stratosphere The in-flight calibration system of GLORIA consists of two identical high-precision blackbodies, independently stabilized at two different temperatures. The GLORIA blackbodies have a large optical surface (6mm x 6mm) with an emissivity of , a spatial thermal uniformity of better than 0 mk and temperature stability of 0.6 mk/min. With the achieved calibration uncertainty of less than 0.3 % GLORIA provides excellent 3D images of the atmosphere. Suggested improvements will lead to even better results. 5

26 CALCON Technical Conference Utah State University, Logan, UT, USA August 4, 04 Acknowledgement: Part of this work has been supported by the European Metrology Research Programme (EMRP) within the joint research project Metrology for Earth Observation and Climate (MetEOC). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the EU. 6