LWP Radiometer Series
LWP, LWP-U90, LWP-U72+82, LWP-90-150 Liquid Water Path Radiometers
These radiometers are used for the remote sensing of integrated water vapor (IWV) and Liquid Water Path (LWP). Both quantities give column-integrated (total) values rather than vertically resolved profiles.
The RPG-LWP model is the standard two-channel microwave radiometer typically used for this purpose. Upgraded versions (RPG-LWP-U90, RPG-LWP-U150, RPG-LWP-U72+88) extend the sensitivity to small amounts of LWP (e.g., thin clouds) by adding one or two higher frequency channels. High-frequency two channel versions (RPG-LWP-90-150) are optimised for thin cloud and snow observation.
Areas of Application
- Liquid water path (LWP) measurements
- Integrated water vapour (IWV) measurements
- Attenuation monitoring
- Beacon experiments
- Cloud observations
- Climate monitoring
- Satellite tracking (GPS, Galileo)
Technical Specifications
| Paramter | Specification |
|---|---|
| System noise temperatures | <350 K typical, <600 at 90 GHz |
| Radiometric resolution | 0.1 RMS @ 1.0 sec integration time |
| Channel bandwidth | 200 MHz @ 40 GHz, 2 GHz @ 72 to 90 GHz |
| Absolute system stability | 0.5 K |
| Radiometric range | 0 – 800 K |
| Frequencies | 23.8 + 31.4 (36.5, 72, 82, 90, 150 optional) |
| Polarisation | 1 linear |
| Absolute calibration | Automatic sky-tipping, liquid nitrogen |
| Internal calibration | Gain: internal Load + noise diode injection |
| Receiver/antenna thermal stability | Accuracy < ±0.015 K |
| Gain nonlinearity error correction | Automatic, four point method |
| Brightness calculation | based on exact Planck radiation law |
| Integration time | ≥1 second for each channel |
| Data interface | RS-232, 115 kBaud, fibre optical |
| Data rate | 9.5 kByte/s, RS-232 |
| Instrument control | Industrial PC (Pentium) or Web-Interface |
| Housekeeping | all system parameters, history documentation |
| Optical resolution | HPBW: <3.6° (≤2° at 72 GHz and above) |
| Side-lobe level | <-30dBc |
| Steering / positioner system | elevation: -90° – +90° azimuth: 0° – 360° <1° resolution, full software control |
| Pointing speed | Elev. 45°s (0.6° res.), azi. 20°s (0.1° res.) |
| Operating temperature range | -40°C to +50°C |
| Operating humidity range | 0 – 100 % |
| Power consumption | <200 Watts average, 400 Watts peak |
| Input voltage | 100-230 V AC, 50 to 60 Hz |
| Weight | 70 kg for radiometer module (stand: 30 kg) |
| Modularity | Standard two-channel systems may be upgraded to have one more frequency band |
Features
- Direct Detection Channels
- High temporal resolution (1 second), spatial resolution <4° HPBW
- Automatic calibration with sky-tipping (software controlled)
- History of calibrations, post-processing possible
- Elevation scanning. With azimuth positioner option: Fully steerable
- IWV (integrated water vapour) and LWP (integrated cloud liquid) full sky maps (350 samples / 5 min.)
- Determination of cloud coverage and monitoring of abrupt changes in the 3D humidity field
- Immune to RF interference below reception bands (e.g. radio transmitters, mobile phones etc.),
- direct detection receiver layout
- Purely passive operation, no internal oscillators or other RF sources (EMI/EMC compliant)
- Extremely short calibration cycles (sky tipping 2 minutes, LN2 also 2 minutes), complete internal auto-calibration systems including noise sources (noise switching, gain calibration) and Dicke switches (system noise temperature calibration)
- Rain protection of microwave windows
- Fiber-optical data cable for lightning protection and secure data transmission
- Operating software for radiometer includes:
- Remote Operation (web-server application)
- Detailed instrument status and control
- Automatic recovery after power failures
- User defined schedules for measurements and calibration
- Internal data file backup system
- Satellite Tracking (GPS data from receiver and RINEX orbit parameter files)
- User interface for complex scan pattern definition
- Level-0 voltage raw data
- Level-1 calibrated brightness temperature data
- Level-2 retrieved products data (LWP, IWV)
- Data formats: Binary, netCDF, ASCII, BUFFR
- Data manipulation and display, time series, analysis
- Housekeeping data
- Data quality checks / quality flags
- Detection and removal of RF Interferences
- Free software updates from FTP server
- North-alignment by software feature (sun-tracking plus GPS)
- Blower system for removal of rain-drops from radome window
- Heater system (1.8 kW) preventing formation of dew (condensation of water and ice) on radome
- GPS clock and receiver
- Rain detection sensor
- Sensors for pressure, temperature, and relative humidity
- Master / Slave tandem operation of two radiometers, forming one virtual instrument
- Options:
- channels at 23.8, 31.4, 72.5, 82.5, 90, 150, 225, 350, 448, 664 GHz
- Retrieved data types:
-
- Liquid Water path (LWP)
- Integrated Water Vapor (IWV)
- wet delay
- dry delay
- Documentation:
- Technical Note (brochure) on LWP Radiometers RPG Standard MWR Installation and Maintenance Manual RPG Standard MWR Software and Operations Manual RPG Standard MWR Technical Specifications and References RPG Standard MWR Guide to Measurements and Deployment
