NAMMA Two-Dimensional Stereo Probe and Cloud Particle Imager

Table of Contents

Introduction

This Cloud Microphysics dataset consist of data from two probes used to measure the size, shape, and concentration of cloud particles; the two-dimensional stereo probe (2D-S), and the cloud particle imager (CPI). Both of these probes measure particle size distributions and derives extinction, particle concentration, ice water content and particle shape. Both probes provide hi-resolution black and white images of cloud particles. The 2D-S probe will more reliably image particles from 10 microns to 1.28 mm at speeds up to 225 m/s than older technology probes. The CPI used was a new version which has twice the data rate of older units. While the CPI probe provides spectacular imagery of the ice particles, its accuracy in measuring PSDs has yet to be established.

These data files were generated during support of the NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign, a field research investigation sponsored by the Science Mission Directorate of the National Aeronautics and Space Administration (NASA). This mission was based in the Cape Verde Islands, 350 miles off the coast of Senegal in west Africa. Commencing in August 2006, NASA scientists employed surface observation networks and aircraft to characterize the evolution and structure of African Easterly Waves (AEWs) and Mesoscale Convective Systems over continental western Africa, and their associated impacts on regional water and energy budgets. For more information about the NAMMA Campaign, go to the NAMMA web site: http://namma.nsstc.nasa.gov/

Both the 2D-S and the CPI are manufactured by Spec, Inc. of Boulder, CO. Complete information on these and other atmospheric science instrumentation products can be found at the Spec homepage: http://www.specinc.com/

2D-S

The 2D stereo (2D-S) probe, a relatively new optical imaging instrument, utilizes two laser beams that cross at right angles in the middle of the sample volume. The overlap region where the two laser beams intersect defines an area where two orthogonal views of particles are obtained, which improves sample volume boundaries and sizing of small (less than 100 µm) particles as compared to conventional optical array probes. The use of two high-speed, 128-photodiode linear arrays allows the 2D-S probe to produce shadowgraph particle images with 10-µm pixel resolution at aircraft speeds up to 250 m s^-1. The stereo views of particles in the overlap region can also improve determination of the three-dimensional shape of a particle. Features of this probe are:

• Two 128-photodiode linear arrays work independently as high-speed and high-resolution optical imaging probes.
• Captures two-dimensional images of particles passing through sample volume where laser beams overlap.
• The region where the beams overlap uniquely defines the depth-of-field (and thus the sample volume) for small particles.
• Response time is 10 times faster than the 2D-C.
• Particles as small as 10 microns imaged at 200 m/s.
• Greatly improved determination of sample volume and sizing of small particles less than 100 microns.

CPI

The Cloud Particle Imager (CPI) provides particle imagery over a range of sizes from 20 to 2000 microns with a 2-micron resolution. The CPI system contains a particle detection system (PDS), and a laser imaging system. The PDS consists of two continuous-wave laser diodes with beams that are shaped into ribbons 2.4 mm wide and 0.5 mm thick. The intersection of the two PDS beams defines the sample volume of the instrument. The imaging system consists of an imaging laser and a million-pixel digital camera. When a particle passes through the intersection of the two laser beams, the imaging laser is pulsed and an image of the particle is cast on the CCD of the digital camera. The PDS counts particles that are transit-time qualified and particle concentration is determined by dividing particle counts by the sample area times true airspeed. The system is controlled by the data system computer and electronics.

The CPI records high-resolution (2.3 micron pixel size) digital images of particles that pass through the sample volume at speeds up to 200 m/s. CCD camera flashes up to 75 frames per second, potentially imaging more than 25 particles per frame.

Data files are of three types, and examples are shown below:

namma_2DS_yyyymmdd_H_DC8.txt
namma_2DS_yyyymmdd_V_DC8.txt
namma_CPI_2yyyymmdd_DC8.txt

where,

namma = the campaign name
2DS and CPI = the instrument (probe) type
yyyymmdd = the year, month and day
H = horizontal data channel
V = vertical data channel
DC8 = type of aircraft instrument was installed on.
txt = shows that these are tab delimited text files.

Data consists of tabular data files from both the 2D-S and the CPI. The 2D-S probe has data files for both the horizontal and vertical channels. Each file has information in the header which explains the specifics of the data and the format.  Listed below is an example of the 2D-S horizontal channel data format by column number:

2D-S H-channel data format by column number:

1) Time is start-time in seconds since midnight.
2) The percentage of images accepted for processing by method 4.
3) A warning, the number of timing irregularities occurring during this second.
4) Concentration (method 4) #/L.
5) Area per unit volume in units mm2/L (method 4). Extinction in units 1/Km may be obtained by multiplying by 2.
6) Liquid Water Content (method 4) g/m3.
7) Number of images smaller than 50 µm accepted for method 4 processing.
8) Number of images larger than 50 µm and smaller than 250 µm accepted for method 4 processing.
9) Number of images larger than 250 µm accepted for method 4 processing.
10-70) Bin concentrations method 4 in units #/L/µm.
71-131) Bin concentrations method 6 in units #/L/µm.
132) Bin concentration method 1 for the 265 - 285 µm size bin #/L/µm.
133) Bin concentration method 1 for the 285-305 mµ size bin #/L/µm.
134) Bin concentration method 1 for the 305 - 325 µm size bin #/L/µm.
135) Number of images smaller than 265 µm accepted for method 6 processing.
136) Number of images larger than 325 mµ accepted for method 6 processing.

Browse Images

The 2D-S browse image files are PNG image files, and are in the following format:

VDyyyymmdd_hhMMss_nnnnnn.png

where,

yyyy=year
mm=month,
dd=day,
hh=hour
MM=minutes
ss=seconds
nnnnnn= nanoseconds

NOTE:

In each png file, at the bottom of the strip is same time stamp of the first image, but expanded to nanoseconds.  At the right side of the strip is the time of the last image in nanoseconds.  The times of the images in between the first and last image in a strip fall in between these two times.  In high particle concentrations, such as in cloud drops, all the images on one page could occur within one microsecond.  There are too many images in a file to time stamp each one, but each image has a time stamp in the raw data file.  Also, please be advised that only the first 20 images in each second are printed out in the NAMMA archives.  If the aircraft is in mixed-phase cloud, you may not be able to determine this from the images, as it is likely that the first 20 images will all be cloud drops.  If you want to do more detailed analysis of 2D-S data you would need the raw data files and the IDL processing programs

References

Baker, B. A., and R. P. Lawson, 2006: In situ observations of the microphysical properties of wave, cirrus and anvil clouds. Part I: Wave clouds. J. Atmos. Sci., in press.

Mazin, I. P., A. V. Korolev, A. Heymsfield, G. A. Isaac, and S. G. Cober, 2001: Thermodynamics of icing cylinder for measurements of liquid water content in supercooled clouds. J. Atmos. Oceanic Technol., 18, 529–542.

R. Paul Lawson,  Darren O’Connor,  Patrick Zmarzly,  Kim Weaver,  Brad Baker,  Qixu Mo, and Haflidi Jonsson: The 2D-S (Stereo) Probe: Design and Preliminary Tests of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe. Journal of Atmospheric and Oceanic Technology, Article: pp. 1462–1477

Heymsfield, A. J., A. Bansemer, P. R. Field, S. L. Durden, J. Stith, J. E. Dye, W. Hall, and T. Grainger, 2002: Observations and parameterizations of particle size distributions in deep tropical cirrus and stratiform precipitating clouds: Results from in situ observations in TRMM field campaigns. J. Atmos. Sci., 59, 3457-3491

The data producer is:

Paul Lawson
Spec Inc.
plawson@specinc.com

To order these data or for further information, please contact:

Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/