1. Introduction

ATS-6UCLA Fluxgate Magnetometer

R.L McPHERRONP.J. COLEMAN, Jr.R.C. SNAREInstitute of Geophysics and Planetary PhysicsUniversity of CaliforniaLos Angeles, Calif. 90024

Abstract

A summary of the design of the University of California at Los

Angeles' fluxgate magnetometer is presented. Instrument noise in

the bandwidth 0.001 to 1.0 Hz is of order 85 my. The DC field of

the spacecraft transverse to the Earth-pointing axis is Sx = 1.0

± 2.1'y, Sy = -2.4 + 1.3-y. The spacecraft field parallel to this axis is

less than 5y. The small spacecraft field has made possible studies of

the macroscopic field not previously possible at synchronous orbit.

At the 960 west longitude of Applications Technology Satellite-6

(ATS-6), the Earth's field is typically inclined 300 to the dipole axis

at local noon. Most perturbations of the field are due to substorms.

These consist of a rotation in the meridian to a more radial field

followed by a subsequent rotation back. The rotation back is

normally accompanied by transient variations in the azimuthal field.

The exact timing of these perturbations is a function of satellite

location and the details of substorm development.

Synchronous orbit is in many ways an ideal location tomonitor a large variety of important magnetospheric phe-nomena. First, because a satellite in this orbit is fixed in themain field, all field changes are due to sources external tothe Earth. Second, since a satellite in this orbit makes thesame complete circuit of the magnetosphere every day, it ispossible to obtain a statistical picture of the occurrence ofvarious phenomena. Third, the main field at this location issufficiently weak that it does not cause difficulties inmeasuring small changes, but is still strong enough to bewell ordered and to organize the motion of charged par-ticles.

Important phenomena which can be monitored with amagnetometer on a satellite in synchronous orbit can bedivided into two classes: changes due to macroscopic cur-rent systems, and hydromagnetic waves. The first class in-cludes the magnetopause boundary currents, the ringcurrent, the tail current, and field aligned currents couplingthe magnetospheric plasma to the ionosphere. The secondclass includes a variety of ULF wave phenomena aboutwlhose generation very little is presently known.

The primary objective of the University of California atLos Angeles' (UCLA) fluxgate magnetometer on Applica-tions Technology Satellite-6 (ATS-6) is to add a body ofempirical data pertaining to the magnetic field at synchro-nous orbit. A secondary objective is to monitor continu-ously this field in order to provide input data for models ofthe time-varying configuration of the magnetosphere.Specific goals within the primary objective concern theproperties of the magnetosheath; the properties of themagnetopause; the interaction of the solar wind with thedayside magnetosphere and the geomagnetic tail; thechanges in field caused by magnetospheric substorms; thedevelopment of the ring current; and the properties ofhydromagnetic waves in these various regions of space.

I1. Instrument Design

Manuscript received August 1, 1975. Copyright 1975 by IEEETrans. Aerospace and Electronic Systems, vol. AES-1 1, no. 6,November 1975.

This work was supported by the National Aeronautics and SpaceAdministration, under contract NAS 5-11674.

R.L. McPherron and P.J. Coleman, Jr., are also with the Departmentof Geophysics and Space Physics, University of California, LosAngeles, Calif. 90024.

The ATS-6 magnetometer is a three-axis fluxgate mag-netometer that employs an automatic digital offset system.The instrument consists of five subsystems: the sensor, thebasic magnetometer, the field offset system, the in-flightcalibrate system, and the power supplies. The magnetom-eter is nearly identical to that used on the Orbiting Geo-physical Observatory-5 (OGO-5) spacecraft [9] and similarto the ATS-1 magnetometer [1], [101. Further develop-ments of this instrument have been described [3], [7].

The sensor assembly houses the three fluxgate sensors inan orthogonal array. The sensors are Forster elements thatwere modified to reduce their size and weight. Auxiliarywindings were wound on each sensor for the feedback andoffset currents.

The basic magnetometer incorporates feedback to im-prove linearity and gain stability. The dynamic range of thebasic magnetometer is ±16y. A measured noise spectrum

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-ll, NO. 6 NOVEMBER 19751110

for the prototype instrument is shown in Fig. 1. The out-put of the basic magnetometer is digitized by a 9-bit con-verter in which the least significant bit represents y.

The offset field generator extends the dynamic range ofthe instrument without sacrificing the resolution of thebasic magnetometer. This is accomplished by applying afield at the sensor opposite to the ambient field sufficientto keep the basic magnetometer within its linear dynamicrange. The localized fields are generated by the offset fieldgenerator, which supplies stable currents in discrete steps toan auxiliary coil wound around the magnetometer sensor.

Fig. 2 is a block diagram illustrating the importantfeatures of a basic magnetometer with offset field gen-erator. The level detectors indicate an off-scale condition ofthe basic magnetometer. When this occurs, counts are eitheradded to or subtracted from the up-down counter. Eachbinary in the up-down counter drives a switch of a ladder-adder type digital-to-analog converter (R/2R resistor net-work). The output of the ladder-adder is a linear functionof the state of the up-down counter. This output is appliedto the coil driver circuit through a trimming resistor RT.The amplifier is biased at 2 VR, the reference voltage, bythe resistor divider network connected to the noninvertinginput. With the offset winding connected in the feedback ofthe operational amplifier, the current I through the windingis equal to ( 2 VR - V/(R +RT), no matter how the coilresistance changes. V is the output voltage of the ladder-adder, R is the characteristic resistance of the ladder, andRT is the trimming resistor. Since the operational amplifieris biased at midscale, the current reverses direction as Vpasses through 2 VR. When the output of the basic magne-tometer activates either level detector, the offset fieldgenerator applies an incremental offset field to the sensorsuch that the basic magnetometer output is returned tocenter scale.

The offset field generator applies field in steps of 1 6y.There are six binary steps in the offset system that provide64 offset levels, giving a dynamic range of - 512y to +496y.The field reading for each axis is the algebraic sum of theoffset and the basic magnetometer reading.

111. Instrument Performance

The ATS-6 spacecraft was successfully placed in orbit onMay 30, 1974. The UCLA fluxgate magnetometer wasturned on shortly after launch to monitor any rotations ofthe spacecraft which occurred during initial stabilization.The magnetometer has been operating almost continuouslyever since. Initial observations indicate that the DC field ofthe spacecraft at the magnetometer is very small. Noisespectra on quiet days show that AC spacecraft fields arealso small. To date, the only operational anomalies detectedare a few spurious calibrations and occasional high-frequency noise on the Z-axis sensor. Whether this noise isof instrumental or spacecraft origin has not been deter-mined.

lo10 -10

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0

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Fig. 1. Composite noise spectra for the prototype ATS-6 magne-tometer. The low-frequency spectrum was calculated using 10241 0-s samples and 22 degrees of freedom. The high-frequency banddiffers only in the use of 1-s samples.

TELEMETRYOUTPUT

OFFSETCOIL

SENSOR

Fig. 2. Block diagram illustrating the method used to extend the+16y range of the basic magnetometer to ±512y.

Upper limits on the DC field of the spacecraft at themagnetometer location have been established in several dif-ferent ways. First, the field observations are in relativelygood agreement with a recent model of the magnetic field[51. This model predicts a variation in field orientationbetween 350 and 550 of the dipole axis [6]. As shown, inSection IVC, in the discussion of Fig. 9, this is very close tothe observed range.

Pitch angle measurements by scanning spectrometers onthe same spacecraft also indicate that the measured fielddirection is very close to the direction of the ambient field.Pitch angle errors are less than 40 [4]. This conclusion isbased on the observation of intense field aligned fluxes of9-keV electrons whenever field perturbations make it pos-sible for the University of California at San Diego (UCSD)detector to look along the local field.

Similar results have been reported by Walker [ 12] whohas observed that pitch angle distributions for energeticelectrons based on the observed field are peaked within 2°or 30 of 900. Taking into consideration the large range ofdirections of the ambient field, these observations suggestthe magnitude of the spacecraft field must be less than 1 Oy.

The magnetic field observations themselves suggest thatthe field perpendicular to a magnetic meridian containingthe spacecraft is much less than 10y. Observations at local

McPHERRON: MAGNETOMETER

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Fig. 3. Two components of the spacecraft field perpendicular to theEarth-pointing axis of the spacecraft. Plotted values were deter-mined as a function of time during a spacecraft roll on February 2,1975.

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Fig. 4. Spectra of the magnetic field during a quiet interval onJune 7, 1974 (01-02 UT). This time precedes the turn-on of thevarious particle experiments which produce some interference at

discrete frequencies.

noon on quiet days give a dipole D component of nearly0Oy. This is expected from symmetry considerations andindicates the spacecraft field along the X-axis sensor is oforder Iy.

Results obtained during a roll of the spacecraft on

February 2, 1975, also inidicate the spacecraft field trans-verse to the Z axis (Earth pointing) is small. Fig. 3 showsthe calculated center of curvature of the locus of themeasured field during the spacecraft roll. To obtain theseresults the observations made by the X and Y sensorsduring the roll were bandpass filtered to remove all natural

variation of frequencies other than that caused by the roll.A running calculation of the center of curvature was thenmade by numerically differentiating the filtered data.These results indicate that the spacecraft field transverse tothe Z axis is Sx = 1.0 ±2.lyand Sy = -2.4± 1.3y.

The AC field of the spacecraft is also very small over thebandwidth of the magnetometer. Fig. 4 is a spectrum of themagnetic field obtained on a quiet day prior to the turn-onof the particle experiments. The dashed line approximatesthe noise spectrum of the most quiet sensor in the proto-type instrument, shown previously in Fig. 1. After 0.5 Hzthe spectra from the X and Y sensors of the flight instru-ment are about equal to the best prototype sensor. Belowthis frequency the spectra exceed the prototype noise level,but are no longer inversely proportional to frequency. Atthese lower frequencies the signal is probably of naturalorigin. An upper limit to the AC noise of the flight sensorsis 85 my rms in the bandwidth 0.001 to 1.0 Hz.A similar spectrum acquired on a quiet day after turn-on

of the particle experiments contains several spectral lines.The strongest of these occur at the first and secondharmonic of 314-s period and are due to the pitch anglescan mechanism in the UCSD experiment. Additional linesoccur at odd harmonics of 32 s (half the duration of atelemetry sequence). The origin of these has not yet beenidentified.

To date only one serious problem has been encounteredin the operation of the magnetometer. Sporadically, highl-frequency noise (f> 0.1 Hz) is observed on the Z-axissensor. The rms power associated with this interference is90 my, considerably greater than the 30-m-y rms noise ofthe sensor itself. Possible origins of this interference includethe spacecraft, other experiments, or the sensor itself.

Another problem which has seriously delayed proc-essing of the magnetometer data is associated with the atti-tude/orbit determinations. The initial data provided on theexperimenter's data tapes have been found to contain quasi-periodic fluctuations. These fluctuations produced oscilla-tions in the transformed field data which made it nearlyirnpossible to study harmonic waves. This problem hasrecently been solved, and corrected attitude/orbit data are

presently becoming available.

IV. Initial Scientific Results

During the first year of operation, data analysis has beenconcentrated on the macroscopic field and its changes withmagnetic activity near the summer solstice. Some work hasalso been carried out on spectral analysis of ULF waves, butthis effort has been handicapped by the UCSD interferenceand the attitude/orbit problems previously mentioned. Wepresent a brief report of the results of these studies.

A. The Median Magnetic Field at ATS 6

The magnetic field at synchronous orbit is dominated onthe dayside by compression due to the solar wind and onthe nightside by the perturbations due to the tail current.

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS NOVEMBER 1975

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Fig. 5 is a schematic drawing illustrating the geometry ofthe magnetic field at ATS-6 at local midnight (-0615 UT).The satellite is located in the geographic equator in a mag-netic meridian close to that containing the dipole and rota-tion axis. The H axis of dipole coordinates is antiparallel tothe Earth's dipole axis, the D axis is perpendicular to hr anda radius vector through the satellite, positive eastward. TheV axis, positive outwards, completes the orthogonal right-handed system.

The field at ATS-6 at local midnight is considerablyinclined inward toward the Earth as a result of distortionsdue to the tail current. During substorms this inclinationfirst increases as the tail current grows stronger and movesEarthward. Changes in the field due to this behavior areprimarily in the V and H components which both decrease.Midway through a substorm, both V and H rapidly returnto their quiet values. Closely associated with this suddenincrease are transient disturbances in the D componentapparently associated with field aligned currents. The signof these disturbances changes near local midnight.

Effects of substorms are so pronounced in the nightsector that the average or median field is dominated by theeffects of substorins described above. Fig. 6 compares theaverage of three quiet days with the median of the first 40days. While the nature of the diurnal variation is similar onquiet and disturbed days, it is apparent that magnetic dis-turbance systematically lowers the V and H components.It is interesting to note, however, that almost no effects ofactivity are seen in the D component.

From this figure it can be seen that the inclination of themedian field at local noon and midnight is, respectively,350 and 600. The Olson-Pfitzer model [5] predicts 350 and550 [9].

B. Effects of Magnetic Disturbance at ATS 6

The substorm disturbances which lead to the systematicbias of V and H described above are transient in nature.This is strikingly illustrated for the V component in Fig. 7.The disturbances generally occur only in the night sectorwith a slight tendency for premidnight events to be larger.On occasion the magnitude of the disturbance in V is com-parable to the quiet fileld (-75-y).A statistical characterization of substorm disturbances at

the summer solstice is presented in Fig. 8. For each dipolecomponent of the field there are five percentile lines plot-ted versus universal time. From bottom to top these are,respectively, at 10, 25, 50, 75, and 90 percent. The averageof three quiet days occurring in the time interval (June 1-July 20, 1974) have been subtracted from the observations.

The characteristics of the V component mentionedabove are apparent in Fig. 8. Perturbations in V are alwaysnegative, i.e., the field becomes more radial than at quiettimes. Also, the largest disturbances usually occur premid-night. Similar results can be seen for the H component.Seventy-five percent of the time, a magnetic disturbancedecreases the H component. However, about 25 percent of

\ \: °° It I Last closed21J Jt field Lines

Fig. 5. Schematic illustration of the field geometry at ATS-6 nearlocal midnight around the summer solstice. The symbols 14 D, Hlabel the orthogonal axes of the dipole coordinate system.

Midnight Dawn N,,,n1Quiet |

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0 8 1ye 16 20 4

Unliversal Time

Fig. 6. Diurnal variation of the magnetic field observed by ATS-6during the first 49 days of operation (June 1 to July 20, 1974).Heavy lines are the averages of three quiet days and light lines are

the medians of all observations except during magnetic storms.

the time the field is enhanced on the dayside. Also, there isa tendency for larger H disturbances to occur premidnight.

The D component behaves quite differently from V andH. First, it can be seen that at least 50 percent of the timethe field is essentially the same as the quiet field. Only inthe 10-percent and 90-percent lines can systematic effectsbe seen. These show that perturbations in D are positivepremidnight and negative postmidnight.

The foregoing results can be interpreted using the modeldescribed in the discussion of Fig. 5. As magnetic activityincreases, the inner edge of the tail current moves Earth-ward, wrapping around the Earth. The center of this"partial ring current" moves from midnight to earlier localtimes as activity increases. Perturbations due to enhance-ment of such a ring are primarily in the magnetic meridianplane, i.e., in V and H. During such intervals of enhance-ment there are frequent substorms. Statistically these are

centered at local midnight and have associated with themtransient field aligned currents. These flow inward to theauroral oval postmidnight and outward from the oval pre-

midnight causing negative and positive D perturbations inD, respectively.

C. Magnetic Field Variations at ATS-6 During MultipleOnset Substorms

The field variations at a synchronous satellite duringsubstorms can be exceedingly complex. It has been found

McPHERRON: MAGNETOMETER 1113

-75-100

125

150Lo 4 s I 16 20 24

Universal Tiune

Fig. 7. V component observed on all nonstorm days betweenJune 1 and July 20, 1974.

MIDNIGHT DAWN NOON

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to

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0 04 058 12 16 20 24

LJNIVERSAL TIME

Fig. 8. Statistics of the deviation from a quiet day. The five linesshown for each trace are, respectively, from bottom to top 10 per-cent, 25 percent, 50 percent (median), 75 percent, and 90 percent.

by several investigators that substorms consist of a sequenceof expansions [2], [81, [1 1]. Statistically these onsets showa tendency to occur at earlier local time as the substormprogresses. Associated with each onset is a westward travel-ing surge and a westward moving field aligned current sys-tem of the form described above. The timing of disturb-ances at a synchronous satellite is very much a function ofwhere the satellite is located relative to the expansiononset.An example illustrating some of these features is given

in Fig. 9. Vertical dashed lines represent the time of majorexpansion onsets as determined from ground magneto-grams. From the field inclination 0 it is apparent that priorto these major onsets, the field becomes very tail-like,while subsequently it returns to a more dipolar orientation.Also, near the time of the onset there are strong distortionsin the field azimuth 0. These azimuthal distortions corre-

spond to positive D premidnight (at 0630 UT) and negativepostmidnight.A midlatitude magnetogram from the Dallas observatory

near the ATS-6 meridian is shown in Fig. 10. Sudden largeincreases in the H component at 0304 and 0742 UT corre-spond to similar increases at ATS-6. Examination of mag-

netograms from other midlatitude stations clearly show thatthe first major substorm was initiated near the San Juanmeridian at 0254 UT. The expansion subsequently movedwestward with subsidiary onsets at 0304 and 0312 UT.The increase in V and H at the satellite was delayed relativeto the first onset at San Juan. In addition, it can be seenthat the positive D perturbation at ATS-6 was almostentirely over before the perturbations began in V and H.In contrast, at Dallas the positive D perturbation (positivedownwards) occurred in association with the H perturba-tions.A weaker substorm event than those just described was

initiated at 0624 UT (cf. Fig. 10). This event was apparentlyquite localized near the satellite meridian as it cannot beidentified in auroral zone magnetograms from FortChurchill or Great Whale River, Canada, nor is it particu-larly observable in other midlatitude magnetograms. Theevent did, however, cause a temporary field rotation andnegative D perturbation at ATS-6. These were both delayedrelative to the presumed onset.

It seems likely that delays of the type described aboveare due to propagation effects. Pytte et al. [8] have sug-gested each onset corresponds to the formation of a local-ized field aligned current system which propagates west-ward as part of a westward traveling surge. Growth anddecay of the current in the surge as well as motion of thecurrent segments relative to the satellite would cause verycomplex variations in the D component.

Such an interpretation seems to be supported by auroraldata in this case. Fig. 11 is a picture taken by the DAPPsatellite in a pass over the southern auroral zone at 0700UT. A westward traveling surge is clearly apparent somedistance west of local midnight (near the left edge of thepicture). At typical angular velocities for surges (2-3°/min)this surge would have to have been initiated near midnightaround 0624 UT, the time of the onset seen in the Dallasmagnetogram (Fig. 10).

V. Concluding Remarks

The UCLA fluxgate magnetometer on ATS-6 has oper-ated almost continuously since launch. The spacecraft fieldat the magnetometer is very small, thus facilitating studiesof the macroscopic field not previously possible in datafrom synchronous orbit. The AC noise level of the magne-tometer is very low (less than 100 my from 0.001 to 1 Hz),as is AC interference from the spacecraft. In combinationwith a rapid sample rate (8 per second) and a high resolu-tion (j y) the low noise will make possible studies of avariety of ULF wave phenomena.

Initial studies of the macroscopic field have been made.The quiet field observations are in good agreement withpredictions of Olson and Pfitzer [5]. Field inclination atlocal noon is surprisingly large, being of order 300 to thedipole axis. Deviations from the quiet field are mainly dueto substorms. Substorm expansions are normally associatedwith a tail-like field that temporarily rotates toward a more

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS NOVEMBER 1975114

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Fig. 9. Magnetic observations during several substorms on July 14,1974. Vertical dashed lines are major substorm expansion onsets.

Horizontal dashed lines represent quiet day base lines. Vertical arrows and numerals indicate the time and magnitude of onsets recordedat the midlatitude magnetic observatory at Dallas, Tex.

dipolar configuration at the time of an expansion onset.In association with most expansions there are transientvariations in the azimuthal field presumably caused by fieldaligned currents. These currents appear to propagate towarddusk in association with westward traveling surges. The

precise timing of these events is strongly dependent upon

the specific details of the substorm development. Duringmultiple onset substorms magnetic perturbations are

delayed or not seen depending on the location of the satel-lite relative to the center of activity.

McPHERRON: MAGNETOMETER

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Fig. 1 1. Observations of the aurora at 0700 UT, July 14, 1974,made by the DAPP satellite in a pass over the southern auroralzone. The south magnetic pole is near the top center, local mid-night is at the left edge, and west is to the right.

Acknowledgment

The UCLA fluxgate magnetometer on ATS-6 wasoriginally developed at UCLA by R.C. Snare and F.R.George. Further developments and construction were car-ried out by A.H. Plitt of Westinghouse Electric Companyunder subcontract to UCLA. Reduction and handling of themagnetometer data are currently the responsibility of N.E.Cline and L.E. Randerson. The principal investigator of thisproject is P.J. Coleman, Jr. Co-investigators include R.L.McPherron and W.D. Cummings. Magnetometer data fromthe Dallas observatory and auroral pictures were providedby the World Data Center, Boulder, Colo. The auroral dataare made available by the Air Weather Service of the U.S.Air Force.

References

[1] J.D. Barry and R.C. Snare, "A fluxgate magnetometer for theApplications Technology Satellite," IEEE Trans. NuclearScience, vol. NS-13, 1966.

[2] C.R. Clauer and R.L. McPherron, "Mapping the local time-universal time development of magnetospheric substorms atmid-latitudes," J. Geophys. Res., vol. 79, no. 19, pp. 2811-2820, 1974.

[3] W. Gore, "Analysis and design of a fluxgate magnetometer,"M.S. thesis, Institute of Geophysics and Planetary Physics,University of California, Los Angeles, Publ. 78-1445, 1974.

[4] C.E. Mcllwain, "Auroral electron beams near the magneticequator," Department of Physics, University of California,San Diego, preprint, 1975.

[5] W. Olson and K. Pfitzer, "A quantitative model of the mag-netospheric magnetic field," J. Geophys. Res., vol. 79, no. 25,pp. 3739-3748, 1974.

[6] K. Pfitzer, "The expected quiet time magnetic field at ATS-6,"preprint, UCLA, September 1974.

[7] J.J. Power, "A digital offset fluxgate magnetometer for usein remote geomagnetic observatories," M.S. thesis, Institute ofGeophysics and Planetary Physics, University of California,Los Angeles, Publ. 1247-37, 1973.

[81 T. Pytte, R.L. McPherron, and S. Kokubun, "The groundsignature of the expansion phase during multiple onset sub-storms," submitted to Planetary and Space Science, 1975.

[9] R.C. Sanre and C.R. Benjamin, "A magnetic field instrumentfor the OGO-E spacecraft," IEEE Trans. Nuclear Science,vol. NS-13, no. 6, p. 333, 1966.

[10] R.C. Snare and G.N. Spellman, "Digital offset field generatorfor spacecraft magnetometers," Proc. Symp. on Space Mag.Explor. and Tech. (Reno, Nev., August 30, 1967).

[11] R. Wiens and G. Rostoker, "Characteristics of the develop-ment of the westward electrojet during the expansive phase ofmagnetospheric substorms," J. Geophys. Res., vol. 80, no. 16,pp. 2109-2128, 1975.

[12] R.J. Walker, private communication, 1975.

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Robert L. McPherron was born in Chelan, Wash., on January 14, 1937. He received theB.S. degree in physics from the University of Washington, Seattle, in 1959, the M.A.degree in physics from the University of Southern California, Los Angeles, in 1961, andthe Ph.D. degree in physics from the University of California, Berkeley, in 1968.

He is now Associate Professor of Planetary and Space Physics at the University ofCalifornia, Los Angeles. He joined the Space Sciences Laboratory of the University ofCalifornia, Berkeley, in 1963, where he carried out numerous studies of ULF magneticpulsations. In 1968 he became a member of the research staff of the Institute of Geo-physics and Planetary Physics, University of California, Los Angeles, where he continuedhis studies of ULF waves using magnetic field data from the satellites ATS-1 and OGO-5.Since 1969 he has been a member of the faculties of the Department of Planetary andSpace Science and the Institute of Geophysics and Planetary Physics at UCLA. Duringthis time he has been primarily concerned with the magnetic variations associated withmagnetospheric substorms.

Paul J. Coleman, Jr. was born in Evanston, Ill., on March 7, 1932. He received B.S.degrees in engineering mathematics and engineering physics in 1954 and the M.S. degreein physics in 1957 from the University of Michigan, Ann Arbor, and the Ph.D. degree inspace physics in 1966 from the University of California, Los Angeles.

He is now Professor of Planetary and Space Physics at the University of California,Los Angeles, and on the faculties of both the Department of Planetary and Space Scienceand the Institute of Geophysics and Planetary Physics. He joined Space TechnologyLaboratories, Inc., in 1958, where he collaborated in experiments on board the earlyspace probes Pioneers I and 5 and the Earth satellite Explorer 6. From 1961 to 1962 hewas with the National Aeronautics and Space Administration where he headed the Inter-planetary Sciences Program. Since 1962 he has been at UCLA where his research has beenprimarily in experimental space physics, involving experiments on the planetary probesMariners 2, 4, and 5, the geostationary satellites ATS-1 and ATS-6, the eccentric Earthsatellite OGO-5, the lunar subsatellites on Apollos 15 and 16, and most recently theplanetary probes Pioneers 10 and 11.

Robert C. Snare was born in Waco, Tex., on July 23, 1931. He received the B.S.E.E.degree from the University of Texas, El Paso, in 1954 and later did graduate work at theUniversity of Washington, Seattle.

He has had varied aerospace experience which includes circuit design, missile andsatellite testing, and launch systems integration. In 1964 he joined the staff of the SpaceScience Center of the University of California at Los Angeles as a Project Engineer. Whileat UCLA he has participated in instrumentation projects for OGO-5, OGO-6, Apollo sub-satellites 15 and 16, ATS-1 and ATS-6, and is currently working on magnetometers forthe International Sun Earth Explorer Mother and Daughter Satellites and for the PioneerVenus Orbiter.

McPHERRON: MAGNETOMETER 1117