ICE-CAMERA: A new instrument for the study of Polar Ice precipitation

What is ICE-CAMERA?

ICE-CAMERA is equivalent to a flatbed scanner. It was built in order to operate unattended in polar regions for the study of ice precipitation

ICE-CAMERA collects precipitation on a glass plate, and every hour it takes a scan photo of it, with 5 um resolution...

ICE-CAMERA in the lab, inside the "Fisica" shelter of Concordia Base, waiting its installation on the roof.

Each image acquired by ICE-CAMERA (>700 Mb size) is immediately processed by means of a MATLAB software developed at INO. Every ice grain is identified and measured. Several shape parameters are measured and all information for each grain are saved into daily text files. A collage photo collecting the grains, sorted by size, is also produced. On the basis of a previous training of the software, a simple classification of each grain is also attempted as shown in the next pictures. At the end of each scan, the glas plate used to collect precipitation is heated in order to sublimate the grains and prepare the plate for a new collection of precipitation. The ICE-CAMERA operates at -20°C inside the case, while external temperature can fall down to -80°C in the antarctic winter. At present it is the only instrument capable of measuring and analyzing the shape of ice precipitations in Antarctica, as far as I know.

Due to the very low humidity, High Plateau Ice crystals show a limited range of shapes, compared with the wide number of shapes described in the international classification scheme: most crystals are hex columns, hex rosettes, hex bullets, needles and hex plates...

A few "nice" examples of ice precipitation captured by ICE-CAMERA at Concordia in 2012.

In the firs case hex ROSETTES of HEX PRISM and BULLETS dominated, while in the second case also HOLLOW HEX PRISMS were common

...........Explore the Images with the Mouse!!

 

WHAT IS CALCULATED FOR EACH CRYSTAL?

Once identified an ice grain in the original picture, it is converted into a binary image. The xy distribution of the grain pixels is then analyzed by calculating several shape parameters:

The Moments of the xy distribution of pixels of the grain are defined by:

And the central Moments are:

The Normalized, Central Moments are:

On the base of those Moments, Hu introduced 7 Moments which are invariant for translation, rotation and resizing:

Those 7 quantities are calculated in ICE-CAMERA software, together with the following shape parameters:

-Eccentricity': The eccentricity of the ellipse that has the same second-moments as the region. The
eccentricity is the ratio of the distance between the foci of the ellipse and its major axis length. The
value is between 0 and 1. (0 and 1 are degenerate cases; an ellipse whose eccentricity is 0 is actually
a circle, while an ellipse whose eccentricity is 1 is a line segment.)

-EulerNumber: the number of objects in the region minus the number of holes in those objects.
-Circularity = 4Π*area/(perimeter²)
-Roundness=4*area/( Π *(maxD²))
-AspectRatio=maxD/minD
-Solidity=area/convexArea
-CompactNess=√((4/ Π) *area)/maxD
-FormFactor=4Π*area/(perimeter²)

-The first 25 coefficients of polar Fourier analysis of the perimeter of the grain

The above measured quantities create a vector of values for each grain. This vector is compared with a statistics of "training" shapes in order to classify the grain into one of the "training" grain shapes. The entire process here described is automatized.

Examples of Statistics of Shape Parameters

A poutpourri of statistics of grain parameters is here show for the entire month of March 2012, for a total of apprx. 80000 ice grains:

Technical Details

ICECAMERA has a simple electronic hearth composed of a PIC16F877 board which drives the motors, the numerous house-keeping sensors, heaters and coolers, and provides the signals for the GiGE linescan camera. The instrument is placed outside, connected with the processing 64 bit PC by means of a CAT5A cable (camera) and a RS232 connection (for the comunication between PIC and PC). The ICE-CAMERA and electronics were designed and tested in order to work down to -40°C, even if the internal temperature is kept at approx. -20°C:

Basic schematics of the instrument

Every hour the PC GUI of the ICE-CAMERA software (LabView NI) is sent to INO for a check of the health of the system: at present the internet connection of Concordia is not sufficient for a remote control of ICE CAMERA, otherwise possible.

Example of GUI report, sent to Italy every hour together with data