CoSSIR Data Portal

CoSSIR Instrument

During CoSSIR's first science flights in the CRYSTAL-FACE field campaign (July 2002), it had fifteen channels; nine of them (183.3±1, 183.3±3, 183.3±6.6, 220, 380±0.8, 380±1.8, 380±3.3, 380±6.2, and 640 GHz) were horizontally polarized, and the remaining six were dual-polarized (487±0.7, 487±1.2, and 487±3.3 GHz). The receivers at 380 and 640 GHz were generally not stable and radiometric signatures were quite noisy.

For the TC4 field campaign (July-August 2007) for which data is available here, CoSSIR had 11 channels of measurements. Table 1 summarizes the characteristics of this new instrument for TC4. The beam width is about 4° and frequency independent. Two close-coupled external blackbody calibration references at the temperatures of ~250 and ~330 K (which are measured to an uncertainty of ±0.1 K) provide accurate calibration of the radiometric measurements. The CoSSIR's widely separated groups of frequencies at 183.3, 220, 380, and 640 GHz are well suited for the retrievals of Dme (median mass equivalent sphere diameter) and IWP (Ice water path) of cirrus clouds. The dual polarization capability at 640 GHz has the potential of inferring the shape of ice particles. Furthermore, the multi-channel measurements around the water vapor absorption lines of 183.3 and 380 GHz will provide retrievals of water vapor profiles. The temperature sensitivity of the instrument with 100 ms integration time should be less than 0.7 K at all channels and the calibration accuracy will be about ±1.0 K in the Tb range of 200-300 K. Analysis of the instrument characteristics suggests that the accuracy of Tb depression will be on the order of 1 K, and the threshold of IWP detection for particles with Dme ~100 µm will be as low as ~5 g/m2 at 640 GHz (Evans et al, 1998).

Table 1. CoSSIR characteristics

Center Frequency (GHz) Bandwidth (MHz) Trec (K) Noise Figure (dB) NEΔT for 100 ms @ 200K (K) Beamwidth degrees) Polarization
183.31 ± 1 500 1341 7.5 0.22 4 H
183.31 ± 3 1000 1341 7.5 0.15 4 H
183.31 ± 6.6 1500 1341 7.5 0.13 4 H
220 3000 1418 7.7 0.09 4 H
380 ± 0.8 700 3361 11 0.43 4 H
380 ± 1.8 1000 2964 10.5 0.32 4 H
380 ± 3.3 1700 2964 10.5 0.24 4 H
380 ± 6.2 3600 2964 10.5 0.17 4 H
640 3000 4306 12 0.26 4 H and V
874 5000 ~5000 14 ~0.40 4 H

 

During TC4, CoSSIR was programmed mainly to operate in conical scanning mode, in which data in both forward and aft 120° sectors at an 53.4° observational angle were acquired at 10-sec intervals. In the conical scanning mode, the antenna azimuthally rotate at 6 rpm to generate the conical scan while the elevation axis is held constant at the prescribed angle of incidence. Twice during each rotation of the azimuth axis, calibration is performed followed by a cross track scan. The elevation axis is used to rotate the antennas to point at the calibration references and then to sweep the antenna patterns through nadir back to the prescribed incidence angle. Thus, for each flight, three data files (forward-conical, aft-conical, and across-track) are produced and available for users. All data files are in text format and data fields are explained in the header.

Figure 1. Representation of the scan pattern of the CoSSIR instrument, illustrating the forward, aft and crosstrack patterns.

The scan geometry of CoSSIR is software programmable and can be designed to serve the scientific requirements of TC4. A typical conical-scan geometry is shown in the figure above, where the scan pattern is projected onto the Earth's surface. The points on the plot represent center of the beam positions. Two complete scan cycles are shown. The aircraft travels at 200 m/s at an altitude of approximately 20 km. The azimuth axis rotates at a constant 36° per second. Thus, each scan cycle takes 10.0 sec providing contiguous coverage for the conical scan at 10-km altitude for a 4° beamwidth. As shown, the scan pattern starts directly forward of the aircraft. The antenna rotates 60° in azimuth when the first calibration sequence begins. After observing each calibration target for 200 ms, the antenna patterns are scanned across the aircraft track back to 53.6° incidence (programmable) to begin scan aft of the aircraft. Calibration and a second cross-track scan are performed at the end of the aft-side scan. The scan cycle is complete when the azimuth axis rotates the antenna forward of the aircraft. The eventual data files, therefore, consists of conical scans in the forward (CONFWD) and in the aft (CONAFT) directions, as well as cross-track (CROSSTRCK) scans.

Example Flight 07/17/2007

Figures 2 and 3, respectively, show sample brightness temperature (Tb) images and variations along the aircraft path from the CoSSIR flight on July 17, 2007.

figure-3
Figure 2. Pseudo color images of brightness temperatures from CoSSIR flight on July 17, 2007.

figure-4
Figure 3. CoSSIR brightness temperature variations along the ER-2 aircraft flight path in the forward direction at 53.4° observational angle (top three panels). The bottom panel gives the variation of the brightness temperature ratios.

Please acknowledge the following in your papers/conference papers that utilize the data: The CoSSIR (Compact Scanning Submillimeter-wave Imaging Radiometer) experimental team at NASA Goddard Space Flight Center provided the field campaign data.

Please contact Frank Evans (303-492-4994, evans@nit.colorado.edu), if you have questions/problems regarding these data files.

2007 July 17 Data

Data available from the July 17, 2007 flight.

  • CoSSIR20070717_CONAFT.txt.zip - zip, 986.77 kB: Data from conical scans in the aft direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070717_CONFWD.txt.zip - zip, 1.49 MB: Data from conical scans in the forward direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070717_CROSSTRCK.txt.zip - zip, 2.6 MB: Crosstrack scan data file (see description under CoSSIR Data Collection heading on the Data main page for more details).

2007 July 19 Data

Data available from the July 19, 2007 flight.

  • CoSSIR20070719_CONAFT.txt.zip - zip, 897.48 kB: Data from conical scans in the aft direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070719_CONFWD.txt.zip - zip, 894.37 kB: Data from conical scans in the forward direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070719_CROSSTRCK.txt.zip - zip, 1.6 MB: Crosstrack scan data file (see description under CoSSIR Data Collection heading on the Data main page for more details).

2007 August 6 Data

Data available from the August 6, 2007 flight.

  • CoSSIR20070806_CONAFT.txt.zip - zip, 1.69 MB: Data from conical scans in the aft direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070806_CONFWD.txt.zip - zip, 1.67 MB: Data from conical scans in the forward direction (see description under CoSSIR Data Collection heading on the Data main page for more details).
  • CoSSIR20070806_CROSSTRCK.txt.zip - zip, 3.01 MB: Crosstrack scan data file (see description under CoSSIR Data Collection heading on the Data main page for more details).