ELBARA III

Posted by elbara on Apr 4, 2016 in | Comments Off on ELBARA III

ELBARA is an abbreviation from ESA L-Band Radiometer. This radiometer is participating in calibration/validation of SMOS satellite.

ELBARA (from ESA L-Band Radiometer) is passive radiometer, working at ∼1420 MHz (Hydrogen HI line). Due to stricte scientific purpose of this frequency (radio astronomy, satellite communications), the L-Band is protected in this range. For this reason, ELBARA measurements (theoretically) should be clean of various radio frequency interferences (RFI) or other artificial emitters.

The crucial element of the Project is ELBARA (ESA L-band Radiometer). This instrument is usually provided by ESA. On the basis of a loan agreement with ESA, ELBARA passes from one user to another. Despite many attempts, ESA had not found an ELBARA instrument free for disposing to ELBARA_PD project. Due to the lack of the instrument, a corrective action was taken: a separate proposal for ELBARA III fabrication for Poland was submitted to ESA, evaluated and granted. The ELBARA III instrument was fabricated by GAMMA Remote Sensing in Switzerland and transported to Poland in December 2015.
The ELBARA-III radiometer is a further development of the ELBARA II system described in Schwank et al. 2010. Main improvements from ELBARA-II to ELBARA-III are:

1. A new temperature-controlled Radiometer Microwave Assembly (RMA). This assembly contains the Radio Frequency (RF) electronics, Temperature Control System (TCS), and Analog-to-Digital Converter (ADC). All those components are enclosed in electromagnetically shielded and thermally insulated enclosure, sealed against water.
2. There is no longer a recess for the Peltier thermal element. The Peltier elements are located between the baseplate and the heat sink.
3. New TEC thermal controller for the Peltier elements. Set temperature of the RMA, corresponding to the set temperature of the Calibration Assembly (CA), can be set in 1 degree steps. Two fans within the enclosure circulate air to even out temperatures within the enclosure.
4. New Instrument Computer (IC) enclosure. The assembly contains the Power Supply for the radiometer and drive motors, as well as a display panel showing system temperatures and voltages. The instrument computer is a multi-core processor running Ubuntu 14.04 LTS OS. Both enclosures can be oriented in any direction and are weather resistant.
5. New Detector assembly includes detector diodes, amplifier, and low-pass filter and a 24-bit Analog Digital Convertors (ADC). The digitized samples are converted to floating point numbers by the STM32F100 Micro-controller within the detector assembly and transmitted over USB interface to the Instrument Computer (IC). New Python routines have been implemented to read the ADC data stream by the IC.
6. Antenna feed cables have been increased to a length of 1.0 m from 0.3 m and use Type N connectors on both ends. The connector is more rugged and has lower loss than the SMA connectors that were used previously. The coaxial antenna cable type is H+S 406 with approximately the same loss (0.2 dB) as the 0.3 m long cables H+S 106 used in ELBARA II.
7. Addition of 6 dB attenuator at the input of the sub-band filters BPF3a and BPR3b to improve isolation between the filters. Since the filters cover different sub-bands, noise outside the pass-band of each filter is reflected. Since the power splitter is not ideal there is some leakage from one filter to the other. Use of the attenuators at the filter inputs reduces this leakage by 12 dB.
8. Bootloader of the TEC allows upgrading firmware from the IC.