Polarimetric, combined, short pulse scatterometer-radiometer system at 15GHz for platform and vessel application A.K.Arakelyan, A.A.Arakelyan, S.A.Darbinyan, M.L.Grigoryan, I.K.Hakobyan, A.K.Hambaryan, V.V.Karyan, G.G.Hovhannisyan, T.N.Poghosyan, N.G.Poghosyan and S.F.Clifford ECOSERV Remote Observation Centre Co. Ltd. 2 G. Njdeh Str., #24, Yerevan, , ARMENIA Phone: (374 10) / ; Fax: (374 10) s:

Abstract In this presentation a K u -band, dual-channel, polarimetric, combined, short pulse (~25ns) scatterometer-radiometer system is described, for short and middle distance application (from 6m up to 300m), for polarimetric (vv, vh, hh, hv), spatio- temporally coincident microwave active-passive measurements of water surface, soil, snow and vegetation parameters. The minimum operational range of the scatterometer is ~6m.

A K u -BAND SCATTEROMETER- RADIOMETER SYSTEM The principal requirements for a development of the system were : The principal requirements for a development of the system were : Functional and constructive combining both microwave active and passive means of sensing as a single microwave device, providing simultaneous operational peculiarities. Functional and constructive combining both microwave active and passive means of sensing as a single microwave device, providing simultaneous operational peculiarities. Coherent-pulse construction of the scatterometer’s functional scheme, provided high level of decoupling between transmitting and receiving sections, allowed realize short range operational potential beginning from 6m. Coherent-pulse construction of the scatterometer’s functional scheme, provided high level of decoupling between transmitting and receiving sections, allowed realize short range operational potential beginning from 6m.

Transmission of signals at a specified (vertical or horizontal) polarization and receiving both co- and cross polarized components of backscattered radar signal. Transmission of signals at a specified (vertical or horizontal) polarization and receiving both co- and cross polarized components of backscattered radar signal. Possibility for application of developed principles and methods for signal’s forming and processing for aero-space based prototype of the system. Possibility for application of developed principles and methods for signal’s forming and processing for aero-space based prototype of the system.

Time division channeling of scatterometer and radiometer functioning was used for the system’s functional scheme development, to provide their swimmingly interaction. Such a construction allows improve relative accuracy of measurements by cross polarized signals, simplify calibration procedure, and reduce complicity and the value of the system, by using microwave and intermediate frequency modules of the system as common modules, for both scatterometer and radiometer channels.

Scatterometric and Radiometric Channels Operation Time Diagram (short distance application from 6m up to 100m)

Scatterometric and Radiometric Channels Operation Time Diagram (application range from 50m to 300m and more) Pulse Transmission at v pol. Radar Reception at vv and vh pol. Time for Receivers Protection Radar Reception at vv and vh pol. 1ms Pulse Transmission at v pol. 100mks Radiometric reception at v and h pol. The Pulse Duration is 100ns Radiometric reception at v and h pol. Pulse Transmission at h pol. 3mks Time for Receivers Protection Radiometric reception at v and h pol. Radar Reception at hh and hv pol. Time for Receivers Protection Radiometric reception at v and h pol. 100ns

Of cause, time-division channeling of stterometer and radiometer functioning has its shortage connected with a reduction of backscattered signals accumulation (storage) efficiency and with a reduction of radiometers’ integration times. However, for stationary and low speed platform application this fact is not sufficient, if the main requirement for the system’s operation is its work stability and the accuracy of the measured data.

1 – Antenna 2 – Orthomode Transducer 3 – Circulator 4 – Polarization Switch SPDT 5 – Protector 6 – Antenna Switch/Modulator 7 – Four-Port Directional Coupler 8 – Attenuator 9 – Noise Source 10 – Isolator 11 – Low Noise Amplifier 12 – Mixer 13 – IF Pre-Amplifier 14 – 3-dB Splitter 15 – Radiometer IF Amplifier 16 – Synchronous Detector & Integrator 17 – Radar IF Amplifier 18 – Phase Detector and Sample/Hold 19 – Reference Oscillator 20 – Pulse Modulator 21 – Microwave Oscillator (Heterodyne) 22 – Directional Coupler 23 –Power Pre-Amplifier 24 – UP-Converter 25 – Band Pass Filter 26 – Power Amplifier 27 – Sq. Detector 28 – LF Amplifier 29 – Sample/Hold 30 – Check Indicator 31 – Synchronizer 32 – Solver and Recorder A block diagram of K u -band (~15GHz) scatterometer-radiometer

The main technical characteristics of developed microwave devices ParametersRadiometerScatterometer Frequency Band ~15GHz~15GHz Polarization v and h vv; vh or hh; hv Two Parabolic Antennas Gains / Sidelobes 26cm Dish/8cm Focus and 50cm/13cm 25dB / -20dB and 32dB / -23dB 25dB / -20dB and 32dB / -23dB Antenna Beam Width ~6 o and ~3 o Cross-Polarization Isolation Better than -25 dB Receiver’s Bandwidth ~10 % ~3% Receiver’s Noise Factor 350 K ~2.5 dB Sensitivity at 1s ~0.15K ~ – 126dB/W

The main technical characteristics of developed microwave devices (cont …) ParameterRadiometerScatterometer Absolute Accuracy of Measurements ~2 K ~1.5 dB Radar Pulse Duration ~25 ns Radar Pulse Power ~65 mW Minimal Operational Range ~6m Weight & Dimensions ~15 kg / 500 x 380 x 340mm 3 Power Consumption ~200 W

CONCLUSION Thus, a K u -band, dual-channel, polarimetric, combined scatterometer- radiometer system is developed and realized. Thus, a K u -band, dual-channel, polarimetric, combined scatterometer- radiometer system is developed and realized. The developed system allows investigate peculiarities of relationships between power (amplitude) and phase characteristics of the backscattered radar signal and between power characteristics of backscattered radar and emitted proper radio thermal signals of the observed surface or object, at various polarizations, under test-control laboratory and field conditions. The developed system allows investigate peculiarities of relationships between power (amplitude) and phase characteristics of the backscattered radar signal and between power characteristics of backscattered radar and emitted proper radio thermal signals of the observed surface or object, at various polarizations, under test-control laboratory and field conditions. The system may be used as a detector and identifier and will allow to detect and to classify at least 32 types of anomalies, originating on the background due to the changes of the observed surface geo-physical and biochemical parameters. The system may be used as a detector and identifier and will allow to detect and to classify at least 32 types of anomalies, originating on the background due to the changes of the observed surface geo-physical and biochemical parameters.

Acknowledgements The described scatterometer-radiometer system was developed, manufactured and assembled in Armenia by ECOSERV Remote Observation Centre Co. Ltd., under the framework of the Project ARG YE-04 of the US Civilian Research and Development Foundation (CRDF NSMP) in collaboration with Cortana Corporation. Authors express their gratitude to CRDF and Cortana Corporation for their financial support of the planned works fulfillment.

Thank you ! Thank you !

At that, the work while of the system is divided by 1ms time cycles, in which 1% of time period is used for transmission of 10 pulses and for reception, sequentially after each transmission, co- and cross polarized components of 10 backscattered scatterometric signals. 9% of the time period or cycle is used to protect the inputs of the radiometric receivers from the impact of the transmitter. And the remain of the time (90% of the work period) is used for reception proper radio thermal signals of the observed surface at v and h polarizations. The polarization of the transmitted signals may be changed periodically or by pre-assigned order, manually, from the system’s management control panel. The input of the system includes a parabolic antenna, an ortho-mode transducer (polarization splitter), two decoupling Y-circulators, a polarization switcher and two antenna switchers or modulators. The scatterometer was built in compliance with a structure of entire internal coherence system. The microwave oscillator’s (heterodyne) signal at ~5.35GHz is used for generation transmitter’s signals in up- converter, and is used as a local heterodyne signal for feeding the mixers of the receivers. As a source for a reference signal for the up-converter and for a phase detectors, a high stable high frequency oscillator is used at 250MHz. Transmitter’s pulse signals, as an envelope of 10 pulses with a duration of 30ns each, are formed by the pulse modulator from the continuous signals of the reference oscillator. The modulation frequency is 1MHz, and the repetition frequency of the envelope is 1KHz, at a modulation depth ~100dB. Receiver’s switcher SP3T is used as well as a modulator for a radiometer. It protects the receivers input from the transmitter pulse signal and carrier leakage as well. The first two positions of polarization switchers SP3T are used for realization of transmitted and received signals polarizations. The third positions of polarization switchers SP3T and the second position of SPDT switcher are used for switching-on the loops for internal calibration of scatterometric and radiometric channels of the system.

The output signals of the up-converter, through the band pass filter, come to the main (power) amplifier and are emitted at a specified polarization. Received co- and cross polarized components of the backscattered signals are converted by the receivers mixers into intermediate frequency (IF) signals and feeds the inputs of the IF pre- amplifiers. The output of the pre-amplifiers is divided in two parts, which feed inputs of scatterometric and radiometric channels IF amplifiers. The input of scatterometer channel’s IF Amplifier connects with the mixer only during scatterometer operation while. Amplified signals, at a central frequency 250MHz and a bandwidth ±50MH, come to the input of phase detector, from the outputs of which I-Q quadrature components, through the sample and hold, come to the input of the ADC (analog digital converter) and are saved by PC for real time (preliminary) and further (detail) processing. Fetch (sampling) time is equal 20ns, and the sampling instant corresponds to the commencement of the receiving of backscattered signals.

The Dicke radiometers use two reference noise temperature levels in the section of their equivalent loads. Such a construction provides gain and noise insensibility and allow carry out continuous calibration. During radiometers’ work period, the receivers’ inputs, by turns of 1KHz frequency, connects to appropriate antenna outputs and to the equivalent load sections outputs (switched of Modulators) by means of the antenna switcher. Switching times to antenna and to equivalent load are equal and constitutes a half of the radiometer modulation time. Input noise signals for the equivalent load section, for creation of a necessary pilot signal, has a modulation frequency 2KHz. It is generated by a noise generator developed on the basis of 1A404a varactor, worked at an avalanche breakdown condition. Modulated noise signals, converted in the mixer and gain in the radiometer IF amplifier, through a synchronous detector and integrator come to the input of the ADC and in parallel with the scatterometer signals are saved by PC. For radiometric receiver’s internal calibration the second noise generator is used, developed as well on the basis of the 1A404a varactor, worked at an avalanche breakdown condition.