Fact Sheet

Fact Sheet

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Timed patch
Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics

TIMED Doppler Interferometer

TIMED Instrumentation

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Experiment Overview

The TIMED Doppler Interferometer (TIDI) is investigating the dynamics and energetics of the Earth’s mesosphere and lower thermosphere. TIDI measurements allow us to obtain a global description of the vector wind fields, as well as important information on gravity waves, species densities, airglow and auroral emission rates, and noctilucent clouds. TIDI provides basic information about global winds. TIDI also contributes to the study of energetics.

Science Objectives

The TIDI interferometer (or Profiler) primarily measures horizontal vector winds along the Earth’s limb, with a vertical resolution 2.5 km and an accuracy that approaches ~3 m/sec under optimum viewing conditions. The TIDI design allows for 100% duty cycle instrument operation during daytime, nighttime, and auroral conditions. TIDI views emissions from the O2(0-0) Atmospheric band to determine the line of sight Doppler wind.

Description and Specifications

TIDI comprises three major subsystems: four identical telescopes, a Fabry-Perot interferometer with a CCD detector, and an electronics box. Light from the selected regions of the atmosphere is collected by the telescopes and fiber-optically coupled to the detection optics. The four fields of view are scrambled along with a calibration field input and converted to an array of five concentric circular wedges. This input then passes through a selected filter, then through a Fabry-Perot etalon, and is finally imaged onto a CCD via a circle-to-line imaging optic (CLIO) device.

TIDI System

Visual mockup of TIDI layout with two telescopes
TIDI Layout (showing two of four telescopes)
Mass:41.8 kg
Electrical Power:19.32 watts (orbit ave.)
Heater Power:11.0 watts
Data Rate:2494 bits/sec
Observations:winds, temperatures, and density
Wind accuracy:3 m/s (line of sight)
Altitude Resolution:2.5 km
Spectral Range:550 – 900 nm
Lifetime:>2 years

Key Spacecraft Characteristics

Orbital Altitude:625 km Circular
Orbital Inclination:74.1o
Total Spacecraft Weight:660 kg
Spacecraft Size:Mid-Lite class
Launch Vehicle:Delta II 7920

Electronics System

Hybrid Power supply
80C51 (UTMC) Flight computer
Data acquisition
CCD controller
Filter wheel/ shutters/ PWM heaters
Telescope servo amp
Calibration lamp power supply

TIDI Telescope

Telescope Specifications

Off-axis Gregorian
Low scatter optics and baffles
Zenith gimbal

Clear Aperture7.5 cm
Area44.2 cm2
Angular FOV2.5o horiz x 0.05overt
Diagram of a fixed gap etalon
Diagram of CCD chip surface

Profiler Specifications

Fixed gap single etalon Fabry-Perot inferferometer
2 x 8 position filter wheel
Circle to line image converter(CLIO)
Passively Cooled CCD detector
5 x 32 Channels
Clear Aperture7.5 cm
Plate Diameter10.5 cm
Gap2.2 cm

Principal Investigator
Dr. Aaron J. Ridley
University of Michigan
2455 Hayward St.
Ann Arbor, MI 48109
Phone:  (734) 674-5727
Email: [email protected]

Dr. Timothy (Tim) L. Killeen, P.I. until 2008
Dr. Wilbert (Wib) R. Skinner, P.I. 2008-2014
Dr. Rick Niciejewski, P.I. 2014-2020

Web Site

TIDI Key Parameter Summary

Tables 1 and 2 summarize the TIDI measurements for dayside and nightside modes, respectively, by listing the altitude range over which it is possible to obtain useful measurements from each emission.

Table 1. Dayside Measurements

MeasurementFeatureAltitude Range
Vector WindOAtmosphere (0-0) P1560 – 100 km
OAtmosphere (0-0) P970 – 115 km

Table 2. Nightside Measurements

MeasurementFeatureAltitude Range
Vector WindO2 Atmosphere (0-0) P980 – 105 km

TIDI Viewing Geometry
Figure 5. TIDI viewing geometry.

The TIDI telescopes perform limb scans through the terrestrial airglow layers throughout the satellite orbit. TIDI obtains these scans simultaneously in four orthogonal directions: two at 45° forward but on either side of the satellite’s velocity vector and two at 45° rearward of the satellite. These four views provide the measurements necessary to construct the horizontally resolved vector winds as a function of altitude along two parallel tracks, one on either side of the spacecraft. Each vertical scan consists of individual views 2.5° (horizontal, along the limb) by 0.05° (vertical, normal to the limb) in angular size. The vertical altitude resolution of the instrument is 2.5 km, but the altitude spacing between views is adjusted to yield a measurement vertical resolution of half a scale height throughout the limb scan. Each up/down acquisition cycle takes 100 seconds to complete, resulting in a nominal horizontal spacing between profiles of approximately 750 km along the orbit track. The exact time per vertical scan will depend on the mode being run and the integration or dwell time needed at each altitude step. Each up/down scan cycles through a sequence of filter tunings, selecting the optimal emissions to be viewed within each altitude range to allow neutral winds to be retrieved.

For more information on TIMED, access the JHC/APL Space Department website.