GPM Ground Validation Cloud Spectrometer and Impactor (CIP-2DP) LPVEx

Table of Contents

Introduction

This Cloud Microphysics dataset consists 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 can calculate particle by particle dimensions yielding concentrations, extinctions, particle size distributions, ice water contents, and other microphysical properties. 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 probe used was an improved 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 particle size distributions (PSDs) has yet to be established.

Campaign

The Global Precipitation Measurement (GPM) mission Ground Validation (GV) campaign will use a variety of methods for validation of GPM satellite constellation measurements prior to launch of the GPM Core Satellite, which is currently scheduled for July 2013. The validation effort will entail numerous GPM-specific and joint-agency/international external field campaigns, using state of the art cloud and precipitation observational infrastructure (polarimetric radars, profilers, rain gauges, disdrometers). Surface rainfall will be measured by very dense rain gauge and disdrometer networks at various field campaign sites. These field campaigns will account for the majority of the effort and resources expended by Global Precipitation Measurement(GPM) mission Ground Validation (GV).

These data were collected during The Light Precipitation Evaluation Experiment (LPVEx) field campaign, which took place in September and October 2010 in the Gulf of Finland. The mission was to detect and characterize light rain and evaluate their estimates of rainfall intensity in high latitude, shallow freezing level environments. These data will be used to conduct a comprehensive evaluation of precipitation algorithms for current and future satellite platforms.

Both the 2D-S and the CPI instruments 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 Probe

The 2D stereo probe (2D-S) 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:

• Has two 128-photodiode linear arrays working independently as high-speed and high-resolution optical imaging probes.
• Captures two-dimensional images of particles passing through the 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 older probes.
• 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 Probe

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. The CCD camera flashes up to 75 frames per second, potentially imaging more than 25 particles per frame.

File Naming Convention

Data are in daily files of the form:

mmddyyyy_CIPG-2DP.txt

where,

mmddyyyy  - Is the month, day and year of the data
CIPG - Cloud Particle Imager (G version)
2DP - 2D stereo Probe
txt- ASCII files

Browse files are

mmddyyyy_HHMMSS_<probe>.png

where,

mmddyyyy  - The month, day and year of the image
HHMMSS - The time in hour, minute, second
probe - The type of probe (CIPG, 2DP)
png - Portable Network Graphics image file

These browse files are a series of images for both probes. Each image represents one minute of flight time, with the first buffer in each of the 60 seconds of that minute shown.

Data Format

Data are in ASCII format, with tabbed columns. The column are labeled as:

1- Time
2 - Lat
3 - Lon
4 - GeoAlt(m)
5 - Pres(mb)
6 - T(C)
7- Nt(#/m3)
8 - IWC(g/m3)
9 - 19 - (Concentration(m^-4)

NOTE:  These data are non-quality controlled, and come with the following note from the PI:

The txt files contains particle size distributions (merged CIP+2DP), a few bulk computations, and some basic flight level data copied from the Wyoming netCDF files.

A few notes on the txt files:

• Shattering corrections have been made for CIP following Field et al (JTECH, 2006).
• Grey-scale particles were measured at the 50% threshold level.
• All CIP/2DP particles are assumed to be ice. Obviously this is not always the case, so if you are looking for rain DSDs please let me know so I can make adjustments.
• There are a few places where the CIP seems unusually high (e.g. late on 09/16). I'm still trying to figure out what happened there.
• I have only done some spot-checking of the data, so please notify me if you see anything strange.

The data producers are:

Aaron Bansemer
Andy Heymsfield
National Center for Atmospheric Research
Boulder, CO, USA

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: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/