ISEE 3 Radio Mapping Experiment

The principal purpose of this experiment is to map the trajectories of type III solar bursts by determining the angular coordinates of a localized source as a function of frequency and time. The radial distance may be obtained by triangulation with observations from another satellite, or from assumptions about the density of the interplanetary medium.

Two perpendicular dipole antennas are used. A 90 m tip-to-tip antenna in the spin plane of ISEE-3, referred to as the S antenna, sees a signal which is modulated because of the changing aspect of the source due to the spacecraft's rotation. The Z antenna is 14 m tip-to-tip, along the spin axis. From the S measurements, the azimuth and strength of the source are obtained. Comparison of S and Z observations provides the elevation of the source from the spin plane and an estimate of its angular diameter.

Measurements are made in 12 frequency channels, between 30 and 1980 kHz, in each of two bandwidths, 10 kHz (B), and 3 kHz (N). Every 1.5 seconds (which is nearly one-half spin), one measurement of Z and 11 of S are made for one frequency channel in each bandwidth, interleaving B and N observations. This provides nearly the full range of modulation possible from the S antenna. (At data rates lower than 2048 bps, proportionally fewer S samples are taken.) The frequency channel is selected according to a fixed 72 step program, designed to observe each frequency at uniform intervals but with shorter intervals for the higher frequencies. Alternate modes of observation are possible using only the B or only the N bandwidth. The 72-step sequence takes 108 seconds to complete. Self-calibration occurs every 18 hours.

本实验的主要目的是通过确定局部源随频率和时间变化的角坐标，来绘制III型太阳爆发轨迹。通过与其他卫星的观测数据进行三角测量，或基于星际介质密度的假设，可以获取径向距离。实验中使用了两个垂直放置的偶极子天线。ISEE-3卫星自旋平面上的90米长天线，称为S天线，观测到的信号因飞船旋转导致源方向的变化而受到调制。Z天线沿自旋轴方向，尖端到尖端的长度为14米。通过S天线的测量，可以获取源的方位角和强度。S天线与Z天线的观测数据对比，可以确定源相对于自旋平面的仰角及其角直径。
测量在12个频率通道中进行，频率范围在30至1980千赫兹之间，每个带宽分别为10千赫兹（B）和3千赫兹（N）。每隔1.5秒（接近自旋周期的一半），在两个带宽中分别对每个频率通道进行一次Z天线测量和11次S天线测量，B和N观测数据交替进行。这几乎覆盖了S天线可能产生的全部调制范围。（在低于2048 bps的数据速率下，S天线的样本数将按比例减少。）频率通道的选择遵循一个固定的72步程序，旨在以均匀的时间间隔观测每个频率，但对于较高频率，间隔更短。仅使用B带宽或N带宽也可以进行交替观测模式。72步序列需要108秒才能完成。自校准每18小时进行一次。