1. X. Bosch-Lluis 1, H. Park 2, A. Camps 2, S.C. Reising 1, S. Sahoo 1, S. Padmanabhan 3, N. Rodriguez-Alvarez 2, I. Ramos-Perez 2, and E. Valencia 2 1. Microwave Systems Laboratory - ECE, Colorado State University, Fort Collins, CO, USA. 2. Remote Sensing Lab, Dept. Teoria del Senyal i Comunicacions, Universitat Politècnica de Catalunya and IEEC CRAE/UPC, Barcelona, Spain. 3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. E-mail: xbosch@mail.colostate.edu IGARSS’11 – Vancouver, Canada, 29 th July 2011 FR3.T03: Microwave Radiometry Missions and Instrument Performance III

2. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Presentation Outline 1. Motivation 2. Introduction to Atmospheric Sounding 3. New Concept Proposal 4. Theoretical Development 5. Simulation Results 6. Future Lines and Conclusions

3. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Radiometric measurements of the atmosphere provide brightness temperatures according to the radiative transfer equation. Retrieval algorithms are used to obtain information on profiles of atmospheric parameters such as water vapor content (WVC). Weighting functions and in-situ measurements from radiosondes (RAOB) are required to perform such retrievals. Here we propose a new approach to this problem which may enable the development of new solutions to the atmospheric profile retrieval problem. Specifically, the goal of this work is to measure the structure of the radiometric emission from the atmosphere using two antennas separated by a certain distance and pointing to the same point in the atmosphere. Motivation

4. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Atmosphere Layer 1 Layer N (10 km) TCTC Cosmic Background Atmospheric attenuation Atmospheric attenuation (from the layer to the ground) Absorption coefficient Physical Temperature dz ds Assuming a stratified atmosphere and a pencil beam antenna Ground level Atmospheric Sounding I – Radiative Transfer Equation (RTE) Basis Discrete RTERTE

5. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Atmospheric Sounding II – Retrieval Algorithm Linearization Weighting Function (MxN) (Jacobian or Kernel) WVC profile to retrieve (Nx1) M radiometric measurements (Mx1) @ several frequency channels Linearization error Linearization point (measured using RAOB measurements) (Nx1) Linearization point (Mx1) The linearization approximation applies only for a certain period of time. It requires the launch of ROAB periodically. Linearizing the discrete problem for retrieving

6. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Atmospheric Sounding II – Retrieval Algorithm Linearization N is the number of atmospheric layers to retrieve M is the number of uncorrelated channels that the radiometer measures Usually N >M → ill posed problem An information content analysis of the measurement determines the quality of the retrieval, i.e. a trade-off between accuracy and spatial resolution Various inversion methods can be used for retrieving WVC: 1.Newtonian Iteration retrieval 2.Regression retrieval 3.Neural Network 4.Bayesian Maximum likelihood

7. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Atmosphere Layer 1 Layer N (10 km) T CB Ground level Baseline LPF Antenna #1 (x 1, y 1, 0) Antenna #2 (x 2, y 2, 0) (x 0, y 0, z 0 ) z x y New Concept proposal True time delay for measuring at points which have different distance with respect Ant1 and Ant2, and sub-overlapping measurements Measure Brightness temperature using a CROSS-BEAM Interferometer Brightness temperature from different atmospheric volumes could be measured independently, without the cumulative effect of the RTE

8. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Visibility sample: Fringe-washing function Integration variable, spans the whole atmosphere Brightness temperature of the point Theoretical development Distance from antenna 1 and 2 to the integration variable Main differences between this concept and interferometric synthetic aperture radiometer: 1.Narrower antenna beamwidth 2.Only one visibility sample, not a set of visibility samples 3.Adjustable true time delay Visibility sample written in Cartesian coordinates:

9. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Antenna beamwidth and overlapping volume effect Main challenge posed by this technique If the overlapping solid angle decreases in comparison to the solid angles of the beams, the radiometric resolution (standard deviation) of the measurement increases. To retrieve the brightness temperature the cross-beam interferometric measurement must be multiplied by the inverse of Very narrow beams mitigate this effect, then same order of magnitude between the overlapping solid angle and the beams’ solid angles

10. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Spatial Resolution 1/2 Horizontal Spatial Resolution (determined by hardware decorrelation time) The spatial resolution is determined by the bandwidth of both receivers (FWF)

11. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Spatial Resolution 2/2, Horizontal Spatial Resolution Moreover, it allows several measurements in the same beam-overlapping volume by changing the delay between both receivers Beam-overlapping volume (This volume contributes to the measured visibility function.) Outside overlapping volume (This volume does not contribute to the measured visibility function.) 3 sub beam-overlapping volume measurements obtained changing the relative delay

12. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Simulation Assumptions and Considerations Assumptions and considerations for the simulation 1.2D atmosphere for simplicity 2.Stratified atmosphere with dx=dz=33 meters 3.Atmosphere dimensions 10x66 Km (303x2000 voxels) 4.Van Vleck model for absorption coefficients, using RAOB measurements for the water vapor, pressure and temperature profile. 5.F=22.12 and 24.50 GHz the same channels as the CMR-H radiometers CSU, channels suitable for WVC retrieval. 6.Gaussian antenna patterns. 7.Identical and perfectly rectangular response of both systems WVC profile used for the synthetic atmosphere, obtained using a RAOB WVC [gr/m3]

13. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Simulation Results, Vertical Scans 1/3 D=600 m #1 #2 #1 #2 Centers of the overlapping area, scanned sequentially Measured temperatures using the cross-beam interferometer:

14. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Simulation Results, Vertical Scans 3/3 Antenna spacing change D=600 m D=6600 m #1 #2 #1 #2 Measured temperatures using the cross-beam interferometer:

15. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Simulation Results, Horizontal Scans 1/2 Atmosphere attenuation effect D=600 m #1 #2 #1 #2 X axis [m] Height Measured temperatures using the cross-beam interferometer:

16. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Simulation Results, Horizontal Scans 2/2 Measured temperatures using the cross-beam interferometer: D=600 m D=6600 m #1 #2 #1 #2 X axis [m] Height

17. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 Conclusions And Open Issues 1.A new radiometric for retrieving VWC proposed using interferometric cross-beam techniques. 2.The system can measure brightness temperatures independent of the RTE. 3.Spatial resolution depends on: The horizontal spatial resolution depends on the BW. The vertical spatial resolution depends on the antenna spacing and beamwidth Ongoing: Keep on studying this technique to better understand its limitations and constraints. Estimate the radiometric resolution for ±10% error WVC retrieval depending on the altitude. Determinate methods for calibrate different parts of the system Phase Amplitude Offset Radiometric calibration (hot and cold load) Perform retrievals from simulated atmospheres (applying techniques such as “onion peeling” instead of a Weighting function approximation). Retrieval error compressive study

18. © RSLab-UPC & MSL-CSU 2011 IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 THANK YOU !