1. THE ARM PROGRAM NETWORK OF
MICROWAVE RADIOMETERS:
INSTRUMENTATION, DATA, AND
RETRIEVALS
M.P. Cadeddu1 and D.D. Turner2
1ArgonneNational Laboratory, Argonne, IL 60439, USA
2NOAA/National Severe Storms Laboratory, Norman, OK 73072, USA
IEEE International Geosciences and Remote Sensing Symposium
24-29 July 2011 Vancouver, CA

2. US DOE ARM Program Climate
Research Facilities

3. Inside a Facility
GVR MWRP MWR

4. The number of microwave radiometers was
recently expanded to cover the frequency range 22
to 183.31 GHz
MWR: 23.8, 31.4 GHz
GVR: 183.3±1,3,7,14 GHz
MWRP: 22 - 59 GHz
GVRP: 170 - 183.3 GHz
MWRHF: 90,150 GHz

5. MWR MWRHF GVR GVRP
MWRP

6. Higher frequencies have higher sensitivity to
PWV and LWP
tb(cloudy) - tb(clear)
40 200
150 MWRHF
30 150
Brightness temperature (K)
90
31.4
20 100
23.8
50 MWR
10
0
0
0 1 2 3 4 5 6
0 20 40 60 80 100 300
LWP 250
200
183.3±1
150
183.3±3
100 GVR 183.3±7
50 GVRP 183.3±14
0
0 1 2 3
PWV (cm)

7. Current RMS Error for the MWR retrievals is ~ 0.5
mm for PWV and ~0.25 mm for LWP
 Decrease PWV RMSE in the Arctic to less than
10% by using the 183 GHz line
 Decrease LWP RMSE to ~ 0.10-0.15 mm in
all climates by using 90, 150, 170 GHz

8. …However the higher frequencies present
new challenges
In the past 4 years 5 TGARS papers were published that used
ARM data between 50 and 183 GHz to improve microwave
spectroscopy at higher frequencies (1 paper on the 183.3 line
width [1], 2 papers on the microwave water vapor continuum
[2,3], 1 paper on the oxygen line parameters [4], 1 paper on
water dielectric models at [5].)
[1] V. H. Payne, J. S. Delamere, K. E. Cady-Pereira, et al., Air-broadened half-widths of the 22- and 183-
GHz water-vapor lines, vol 46, pp 3601-3617, 2008.
[2] D. D. Turner, M. P. Cadeddu, U. Lohnert, S. Crewell, A. M. Vogelmann, Modifications to the water
vapor continuum in the microwave suggested by ground-based 150-GHz observations, vol. 47, no. 10, pp.
3326-3337, 2009.
[3] V. H. Payne, E. J. Mlawer K. E. Cady-Pereira J.-L. Moncet, Water Vapor continuum in the
microwave vol 49, vol. 6, pp 2194-2208, 2011.
[4] M. P. Cadeddu, V. H. Payne, S. A. Clough, K. Cady-Pereira, and J. C. Liljegren, The effect of the
oxygen line-parameter modeling on temperature and humidity retrievals from ground-based microwave
radiometers, vol. 45, no. 7, pp. 2216-2223, 2007.
[5] M. P. Cadeddu D. D. Turner , Evaluation of Water Permittivity Models From Ground-Based
Observations of Cold Clouds at Frequencies Between 23 and 170 GHz,
DOI:10.1109/TGRS.2011.2121074, 2011.

9. Radiometers Calibration
All radiometers that calibrate with tip curves use an
automated calibration algorithm developed within the
ARM program.
Tip calibration data from 3/11-SGP 30 GHz 1. Voltages, calibration
and diagnostic data
are stored in data files
Tnd and archived.
Days in March 2011 2. Cryogenic calibration
records are kept in a
The tip calibration algorithm is calibration database
fully automated with a dynamic
tracking of the noise diode 3. All datasets can be
temperature and is described in reprocessed if needed
several documents.

10. Data Quality Control
Data from the ARM microwave radiometers are
subject to layers of quality control
 Data quality flags
 Data Quality Office (obvious problems with the data)
 Monthly reviews by mentor and monthly quality
reports
 Segments of bad data are flagged through Data
Quality Reports (DQR)

11. PWV and LWP Retrievals
 PWV and LWP for the MWR at all sites are retrieved with a
statistical algorithm seasonally trained with radiosonde data
(physical retrievals are available at selected site)
 Wide dynamic range:
PWV: 0-10 cm Retrieval uncertainty ~0.5 mm PWV
LWP: 0-3 mm (3000 g/m2) Retrieval uncertainty 0.25 mm
 At the North Slope of Alaska neural network PWV
retrievals from the GVR (183 GHz) are available and
LWP retrievals are in development

12. GVR retrievals at the North Slope of Alaska
Higher frequencies (170-183 GHz) are useful in very
dry conditions during the Arctic winter (PWV < 5 mm)
PWV error percentage %
30 NSA Jan+July 2007
Retrieved LWP distribution %
30
20
20
10
10
0
15
0 10
0 5 10 15 20 25
5
PWV from radiosondes 0
0 20 40 60 80 100 0 20 40 60 80 100
LWP
New PWV retrievals from the
GVR are available LWP retrievals from the GVR
and GVRP are in development

13. Temperature and humidity profiles
 Statistical retrievals of T and H profiles are available at two
ARM sites
 Temporal and vertical resolution trade-off
 Elevated inversions and moisture gradients difficult to resolve
Figure from: J. C. Liljegren, Initial evaluation of profiles of temperature, water vapor, and cloud liquid water from a new
microwave radiometer, 11th Atmospheric Radiation Measurement (ARM) Program Science Team Meeting, Atlanta, Georgia.,
19-23 March 2001.

14. NSA, PWV~ 0.8 cm
10
8
Height (km)
6
4
Azores, PWV~1.8 cm
2
10
0
-60 -40 -20 -5 0 1 2 3 0 50 100 200 8
T(C) WVd g/m3 RH %
6
Height (km)
4
2
0
-50 -30 10 10 0 5 10 0 50 100 150
T(C) WVd g/m3 RH %

15. New generation of 3-channel radiometers
will be deployed in 2011-2012 at all sites
 23.8, 30, 89 GHz
 Improved stability
 Narrower FOV
 2 and 3 channel
retrievals in development
 Gradual replacement
of 2-channel MWRs

16. Data availability
MWR MWRP GVR GVRP MWRHF MWR3C
NSA SGP
Sites ALL NSA NSA ALL
AMF1 AMF1
Frequencies 183.3 ±
23.8, 31.4 22-59 170-183.3 90, 150 23.8, 30, 89
GHz 1,3,7,14
PWVA
PWVA PWVA PWV* PWV* PWV*
Retrievals LWPA
LWPA LWP* LWP* LWP* LWP*
T&H ProfilesA
Statistical Neural Neural Statistical
Algorithm Statistical Physical
Physical Network Network Physical
Availability 1993- 2004- 2006- 2008- 2008- 2012-

17. Summary
The DOE ARM Climate Research Facility has expanded the
network of microwave radiometers to cover frequencies
between 22 and 183.3 GHz. All radiometers are consistently
calibrated and data subject to stringent quality control
The new radiometers were designed to reduce the RMS error of
PWV and LWP retrievals in regions such as the Arctic and in
optically thin clouds
New retrievals involving the use of higher frequencies (90-183
GHz) are in development (some are already available) and will
supplement the standard ARM retrievals (23.8 and 31.4 GHz)
Data and retrievals are freely available for download from the
ARM archives (www.archive.arm.gov)