S-Pol TRMM-LBA Brazil 1999
S-Pol TRMM-LBA Brazil 1999
The images are based upon data that are largely uncalibrated and having only very limited quality assurance procedures applied. Information should be treated as primarily qualitative.
All times shown in the images are in Universal Time Coordinates (UTC, formerly referred to as GMT). UTC varies from local time by 4 hours for S-Pol in TRMM-LBA. Local sunrise is very nearly at 1000 UTC.
The images provided in both the GIF and MPEG format were created using the ATD Solo radar display package. Data are displayed centered upon the radar location. Range rings are shown every 40 km, and azimuth spokes every 30 degrees. An effort has been made to select only full 360-degree surveillance scans, and to provide one scan at an elevation angle of 1.1 degrees, every ten minutes. Rarely, other elevation angles may be used, or there may be more than 10 minutes between successive scans.
There may be periods of missing scans. This does not necessarily indicate missing radar data for these time periods. Rather, the radar may have been performing sampling that did not meet the desired criteria (i.e., the radar may have been doing RHI scans, or scans at other than the desired elevation), or the routine to absorb scans in real time may have failed briefly. An effort will be made to fill in all missing scans, but this will not be done for the first releases of this Quick-Look summary data set. (For TRMM-LBA, S-Pol operated virtually continuously from 16 Jan through 28 Feb, 1999, with only brief outages for maintenance.)
Four parameters were selected for inclusion in the GIF images. These parameters are:
A fifth parameter, velocity, is available only in the MPEG movie files. Each of the MPEG movie files includes two parameters: reflectivity, paired with one of the other four parameters. A total of four MPEG movies are provided for each time period.
Users should review the published literature for the meaning of these various quantities. The parameters were selected as a best-guess of which parameters would be most valuable in determining time periods for further, detailed study; the selection was arbitrary, and the choice can be disputed.
All displayed parameters lack final calibration checks (but it is not expected that any corrections will be large). Reflectivity is unthresholded, but all other parameters are thresholded on received power (horizontal received power for velocity, differential reflectivity and differential phase; vertical received power for linear depolarization ratio).
The linear depolarization field shows frequent evidence of second-trip echoes. These features can be easily removed with automatic thresholding, but were not, in order to mark areas of cross-pol quantities that may be contaminated. The frequency of red values in LDR does not indicate a problem in the radar system. It simply illustrates a fundamental physical limitation of any radar system with a given pulse repetition frequency.
Note that the co-polar radar quantities suffer second trip echo contamination, but based on a characteristic PRF of one-half the PRF of the cross-polar parameters. For S-Pol in TRMM-LBA and PRECIP98, the effective PRF of the co-polar quantities is typically 425, while the cross-polar effective PRF is 850. The higher the PRF, the greater the liklihood of second trip echoes.
Partial beam blockage is evident in the low elevation sweeps at S-Pol. Blockage is at its worst between about 250° through 300° azimuth. Some additional small sectors are partially blocked where individual Brazil nut trees interfere with transmission (despite widespread deforestation, Brazil nut trees are a protected species, and may not be removed).
A test pulse is evident at extreme range in all parameter frames. This test pulse is monitored in real time to assure stability of the system, and will be re-evaluated in post processing. The test pulse is at about 155 km range, and is 2.5 km wide.