For Presentation at BOREAS Conference,
Ellicott City, Maryland, 29-31 March 1995
Exceptionally high cosmic radiation was observed in the southern study area (SSA) of BOREAS during a three-day period in September 1994. The radiation values were observed during aerial surveying to measure the soil moisture along established BOREAS flight lines. Such high input of cosmic radiation is considered to be a rare event, and could affect radiation measurements by other BOREAS scientists. This report has been prepared to discuss how the radiation data were observed and to present information on the temporal and spatial variation in the cosmic radiation.
The National Weather Service (NWS) airborne gamma radiation
system is used in the BOREAS study. For the benefit of those not
familiar with the system a brief description of the NWS airborne
system follows. Primarily the purpose of the NWS system is to
provide information on the energy levels of gamma radiation
emitted from the surface of the earth. The NWS airborne system is
used by HYD-6 of BOREAS to measure the soil moisture (SM) of the
mineral soil, the water content (WC) of the moss/humus layer, and
the amount of standing water (SW) and by HYD-4 to measure the
water equivalent (WE) of the snow cover. The NWS system uses two
NaI(Tl) detectors. The first detector is up-looking and consists
of two 10.2 x 10.2 x 20.3 cm detectors. The up-looking detector
measures gamma radiation having energy levels from 3.00 to 5.12
mev. The second detector consist of five down-looking detectors
of the same size. Photo multiplier tubes associated with the
detectors, provide radiation data for determining a gamma energy
spectrum for each survey.
Counts-per-minute (cpm) values for three radiation windows are derived from the average energy spectrum for each flight line. The radiation windows are the Potassium (40K) window (from 1.37 to 1.57 mev), the Thallium (208Tl) window (from 2.42 to 2.82 mev) and the Gross Count (GC) window (from 0.42 to 3.00 mev). The cpm data for each window, compared to background calibration data values, are used to compute estimates of the SM and WE of the snow cover and other variables. Stripping techniques are used to compute the counts in the K and Tl windows representing the number of uncolided K and Tl gamma radiation counts received by the down- looking detector that originate from the radioactive elements in the ground. The Gross count is a measure of all gammas in its energy window. The observed GC counts from the down-looking detector are corrected for gammas produced by radon and by cosmic radiation using measurements from the up-looking detector.
The final GC values are generally fairly stable and reliable for use with the estimates from the K and Tl windows in estimating SM. In some countries, that do not have the special detectors as does the NWS, only GC counts are used for determining estimates of the SM or the WE of the snow cover.
The standard NWS procedure is to use weighted values of the K, Tl and GC corrected counts to determine final SM and WE estimates. During analyses of the BOREAS airborne radiation data, using the standard NWS weights, very high cosmic counts from the up-looking detector resulted in estimates of negative soil moisture for some of the flight lines during the three days in September 1944. For these particular days the in-situ SM was the lowest observed during the BOREAS study.
During the FIFE experiment conducted near Manhattan, Kansas in 1987 and 1989, revised weighting factors for short flight lines were developed using only the K and Tl windows for estimating SM. The revised FIFE weights have been used to calculate SM estimates for all BOREAS surveys. Thus, the high cosmic radiation readings do not affect the BOREAS estimates of SM. The computed estimates of SM using the revised FIFE weights correlate well with those computed using the standard NWS weights (including the GC window) except for the three-day period in September 1994.
In the BOREAS SSA there are 24 flight lines for the soil
moisture measurement program by HYD-6 (these flight lines and
others are used for the snow measurement program by HYD-4) The 24
flight lines are divided into 90 segments (bins) to provide
measurements on a smaller scale. Not all lines are measured each
day during field operations. Special attention is given to those
flight lines established over or near the primary BOREAS tower
For three days in September 1994 (8th - 10th) many of the cosmic radiation measurements from the up-looking detector for segments of flight lines (bins) in the SSA were significantly greater than all other measurements made during BOREAS. Table 1 is a summary of all up-looking detector counts-per-minute observed during the entire BOREAS study (including measurement over the northern study area and along the transect between the two areas). The first three columns of numbers are those recorded over the SSA by the up-looking detector for the three days in September 1944 when the high radiation was observed. On 8 September 41 bins were surveyed. Of these 24 had high cosmic counts that averaged 1,389 with a standard deviation of 63.9. On 9 September 51 bins were surveyed in the SSA and 30 had cosmic counts that averaged 1,420 with a standard deviation of 37.9. On both days a couple of flight lines with high cosmic values also had 1 or more bin values that were less, but higher (about 500 counts-per-minute) than values for other flight lines that averaged only slightly more than 200 cpm.
On 10 September 40 bins were surveyed and high cosmic radiation cpm (averaged 1,383 with a standard deviation of 40.8) were observed for all bins in the entire SSA. The high counts on these three days contrast sharply with the average cpm of 188 (standard deviation of 20.3) for all other BOREAS measurements (1,643 bins).
Airborne surveys were conducted over the SSA during
September 1993, February 1944, and during July, August and
September 1994. No high radiation values were observed for any
bin of any flight line in the entire BOREAS study area prior to 8
September. Figure 1 shows the SSA area of BOREAS that had high
cosmic radiation on 8 September. For some flight lines, i. e.,
BP102 immediately east of Prince Albert National Park, only 4 of
the 5 flight line bins had high radiation values providing fairly
precise information on the edge of the high radiation. In the
area just east of Candle Lake flight lines CR960 and BP113 had all
high values on 8 September and BP114 just to the north had only
The area of high cosmic radiation increased by 9 September, Figure 2. The high value area included part of additional northern flight lines (BP114, BP117) and extending south and to the east of flight line CR960. However, flight line BP113 to the north of CR960 changed from high to low values.
On 10 September every measured bin in the SSA had high cosmic radiation. No airborne gamma radiation measurements are available after 10 September.
When very unusual measurements of radiation are observed, questions are generally raised pertaining to the accuracy and consistency of the measurements. Often the calibration of the sensors used, changes in observers, different measuring techniques, and different platforms for the radiation sensors are reasons why unusual data are often questioned. In this case, the same pilots, using the same aircraft and the same sensors, conducted all BOREAS surveys. The contrast in the observed cosmic radiation data on the 8th and 9th of September, and the definite patterns shown in Figure 1 and Figure 2, says much about the relative accuracy and consistency of the measured cosmic data.
When the high cosmic counts were encounter the question of
how unusual were the cosmic radiation measurements was raised.
The NWS system using the up- and down-looking detectors has been
operationally used since February 1979. During the past 15 years
records of airborne NWS surveys of more than 1,600 flight lines
covering portions of 25 states and 7 Canadian Provinces have been
stored in an operational data base. The up-looking cosmic
radiation records from approximately 14,000 flight line surveys in
the data base were reviewed and all counts of 500 or greater were
selected (743 cases). None of the 743 cases were observed in
Canada or in the northern tier of US states where large counts had
been thought possible.
The only locations to have the large cosmic counts were flight lines in the states of California, Colorado, Utah and Wyoming, where most of the flight lines are at elevations much higher than those in the BOREAS study area. Of the 743 selected records only 81 cases have values of 800 or more (with a single high value of 1,022 cpm). Cosmic radiation observed at a high elevation would be expected to have higher counts as a result of less atmosphere above the flight line. A simple plot of the average cosmic cpm versus elevation shows a high correlation between the cpm and elevation.
With no observed cases of cosmic cpm greater than should be expected from the cpm versus elevation plot for all 14,000 historical cases, the occurrence of the high radiation valules is very to be very unusual. In a brief discussion with J. Trombka, a NASA Space Physics scientist of Goddard Space Flight Center, he advised that the high cosmic radiation could be a very rarely measured event.
There has not been time to investigate or to discuss the high cosmic radiation values or the patterns that have been observed with many other space and basic physicists. It is noted, that during the BOREAS field campaign in September 1994 heavy auroura borealis activity was observed. J. Trombka suggested that the observed cosmic rays are probably solar protons that originate during solar flares at energy levels of about 100 mev and decrease to the measured values of 3.00 to 5.12 mev due to a process called Brehmstralung. He also said that the cosmic rays would align with the magnetic field lines of the earth and thus arrive at the earth in definite patterns. A retired physicist (C. Fields) hypothesized that the changes in the daily patterns in Figure 1 and Figure 2 could possibly be related to changes in the earth's magnetic field due to small shifts in the magma of the earth. The authors are not space physicists and those who may be interested in learning more about the records or in providing the authors with additional information are cordially invite to contact them.
The occurrence of high cosmic radiation may affect radiation or other measurements by BOREAS investigators. The authors are interested in any studies of0 the effect of the high cosmic radiation on other measurements.
Carroll, T.R. 1981. Airborne soil moisture measurements using natural terrestrial gamma radiation. Soil Sci. 132:358-366.
Carroll, T.R. 1987. Operational remote sensing of snow water equivalent and soil moisture in the United States using natural terrestrial gamma radiation, J. Int., Asso. Hydro. Sci., IAHS Pub.
Carroll, T.R., and M. Allen. 1988. Airborne gamma radiation snow water measurements and soil moisture measurements and satellite areal extent of snow cover measurements: A user's guide, Version 3.0., Office of Hydrology, National Service, Minneapolis, MN.
Carroll, T.R., E.L. Peck, and D.M. Lipinski. 1988. Airborne time- series measurements of soil moisture using terrestrial gamma radiation. Proc.Ann. Conf. Am. Soc. Photogram. Remote Sens., St. Louis, MO
Fritzsche, A. E., 1982. The National Weather Service Gamma Snow System Physics and Calibration. NWS -8201 report, The Remote Sensing Laboratory, E G & G, Energy Measurement Group, Dept. of Energy, Las Vegas, NV, Dec.
Peck, E. L., 1992. Airborne Gamma Radiation Measurements of Soil Moisture During FIFE, Activities and Results, Hydex Final Report, NASA Contract NAS5-30959, April. In FIS.
Peck, E.L., T.R. Carroll, and D.M. Lipinski. 1990. Airborne gamma radiation soil moisture measurements over short flight lines. Sym. on the First ISLSCP Field Experiment, Anaheim, CA, American Meteorological Soc., Boston MA, p. 79-84.
Peck, E. L., T. R. Carroll, and D.M. Lipinski. 1992. Airborne Soil Moisture Measurements for First International Satellite Land Surface Climatology Program Field Experiment, Jour. Geophys. Res. 97, No. D17, p. 18,961-18,967, Nov 30.
Peck, E. L., and A. S. Hope. 1993. Spatial Patterns of Soil Moisture for the FIFE Study Area Derived from Remotely Sensed and Ground Data. Submitted for 2nd FIFE Special Issue of American Geophysical Research Journal of Geophysical Research, May.
DAY DAY DAY ALL 940908 940909 940910 DAYS 1/ SSA AREA w/high counts 2/ AVERAGE 1389 1420 1383 STDEV 63.9 37.9 40.8 NO. 24 30 48 SSA AREA w/low counts AVERAGE 214 233 all STDEV 31.0 53.1 high NO. 14 14 values SSA AREA w/mod counts /4 AVERAGE 479 695 all STDEV 15.8 284.8 high NO. 3 9 values ALL OF BOREAS w/low counts AVERAGE 3/ 3/ 3/ 188 STDEV 20.3 NO. 1643
Notes: SSA =BOREAS Southern Study Area Energy level of GCU detector = 3.0 to 5.12 mev. Measured values are for flight line and segments of flight lines (bins)
- All BOREAS measurements other than high counts on Sep 8-10, 1994 in SSA
- Over 1,000 cpm
- No measurements other than in SSA
- On edge of high count area. Part of flight lines with high counts
Eugene Peck and Tom Carroll