LWP Radiometers

(LWP, LWP-U90, LWP-U72+82, LWP-90-150)

Overview

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.

Applications:

Liquid water path (LWP) measurements
Integrated water vapour (IWV) measurements
Attenuation monitoring
Beacon experiments
Cloud observations
Climate monitoring
Satellite tracking (GPS, Galileo)

Models:

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. For observation of thick clouds and rain we recommend the dual-polarized Rain Radiometer (LWP-Rain).

Model	Frequencies	Applications	Description
LWP	23.8 & 31.4 GHz (23.8/36.5 GHz optional)	Standard two-channel radiometer for estimation of IWV and LWP	The RPG-LWP-XXX series of liquid water path radiometers is meant for measurements of total water vapour (IWV, integrated water vapour) and total cloud water (LWP, liquid water path). Higher sensitivity to low-density (thin) clouds can be achieved by upgrading the standard LWP radiometer with higher frequencies. Atmospheric attenuation measurements (e.g., for beacon experiments) can be performed.
LWP-U90	23.8, 31.4, 90 GHz	Improved sensitivity to thin clouds
LWP-U150	23.8, 31.4, 150 GHz	Improved sensitivity to thin clouds
LWP-U72-82	23.8, 31.4, 72.5, 82.5 GHz	Improved sensitivity to thin clouds, attenuation measurements for data links
LWP-90-150	90 & 150 GHz	Observation of thin-clouds only. Ideal extension of all above radiometers in master-slave mode.

Technical Specifications

Parameter	Specification
IR radiometer option	9.6-11.5 µm band, accuracy 1 K, noise: 0.2 K RMS
LWP	Accuracy: ± 20 g/m^2,, Noise: 2 g/m²RMS
IWV	Accuracy: ± 0.2 kg/m² RMS, Noise: 0.05 kg/m²RMS
Full sky IWV and LWP maps (only with azimuth positioner)	350 points in 6 minutes rapid scanning
Satellite tracking mode	Determines wet/dry delay, atmospheric attenuation and humidity profiles along line of sight for all visible GPS / Galileo satellites in a single scan (2 minutes)
(only with azimuth positioner option)	scanning with RINEX navigation file or direct GPS vector reading from GPS clock
Channel centre frequencies	23.8+31.4 (36.5, 72.5, 82.5, 90, 150 optional)
Channel bandwidth	2 GHz @ 72 to 90 GHz, 230 GHz @ all other
System noise temperatures	< 400 K typical, < 600 at 70 to 90 GHz typical
Radiometric resolution	0.1 RMS typical @ 1.0 sec integration time
Absolute brightness temperature accuracy	0.5 K
Radiometric range	0-800 K
Absolute calibration	with internal ambient & external cold load
Internal calibration	gain: with internal noise standard
	gain: with internal noise standard
	gain + system noise: ambient temp. target + noise
	gain + system noise: ambient temp. target + noise
	abs. cal. of humidity profiler: sky tipping calibration
Receiver and antenna thermal stabilization	Stability better than 0.03 K over full operating temperature range
Gain nonlinearity error correction	Automatic, four point method
Brightness calculation	based on exact Planck radiation law
Integration time	≥ 0.4 seconds for each channel, user selectable
Sampling rate for profiles	≥ 1 sec, user-selectable
Rain / fog mitigation system	Highly efficient blower system (130 Watts), hydrophobic coated microwave transparent window, 1.8 kW heater module preventing formation of dew under fog conditions
Environmental Sensors	On a 1-meter mast attached to the radiometer:
	On a 1-meter mast attached to the radiometer:
	Temperature, pressure, relative humidity
	Wind speed, wind direction
	Wind speed, wind direction
Data interface / rate	Ethernet (TCP/IP)
Instrument control (external PC)	Windows™ System with Ethernet interface
Instrument control (internal)	Embedded PC, controls all internal calibrations, data acquisition, data file backup on 1 GB flash memory, control of azimuth positioner, communication with host, can run measurements independently from host PC
Housekeeping	all system parameters, calibration history documentation
Retrieval algorithms	neural network, linear /nonlinear regression algorithms
Optical resolution	HPBW: ≤ 4° (≤ 2° at 72 GHz and above)
Side-lobe level	<-30dBc
Pointing range / resolution	Elevation: 0° to 180° (0.15° steps), full s/w control
Pointing range / resolution	Azimuth (optional): 0° to 360° (0.1° steps), full s/w control
Pointing speed	45°/sec (elevation), 40°/sec (azimuth, optional)
Operating temperature range	-40°C to +45°C
Power consumption	<120 Watts average, 350 Watts peak for warming-up (without dew blower heater), blower: 130 Watts max.
Lightning protection	Power line: circuit breakers
	Power line: circuit breakers
	Data line: Fibre optics cable (max. length: 1400 m)
Input voltage	90-230 V AC, 50 to 60 Hz
Weight	60 kg (without dew blower)
Dimensions	63 × 36 × 90cm³
Extendibility (master-slave mode)	Any single-polarization std. radiometer
Customization	Frequencies and bandwidth adaptable
Weather station	Lufft WS600-UMB

Center frequencies and channel bandwidth may be customized without a major effort. Any combination of two waveguide-bands in one instrument is possible.