Instruments on board ER-2
Convection in thunderclouds, charging, lightning activity, and the production of energetic radiation are all inter-related processes. To understand how energetic radiation is produced, gamma-ray detectors are fundamental but not enough. Therefore, the ALOFT payload consists in a diverse set of instruments designed to investigate simultaneously all these complementary aspects. The payload includes radiation detectors, optical instruments to image lightning discharges below the aircraft, electric field sensors to probe the cloud charge structure, radars and microwave radiometers to probe the 3D physical structure of the clouds.
Main content
Gamma-ray Detectors
University of Bergen: Bismuth-Germanite detector (UIB-BGO)
The gamma-ray instruments have been modified to accommodate the wide dynamic range required between the modest gamma-ray glow flux and the extremely high peak fluxes in TGFs. In addition, UIB-BGO will be able to provide real time telemetry of gamma-ray observations, enabling detection of glows and subsequent re-flight of glowing thunderstorms within minutes of their observation. This package includes 4 different gamma-ray detectors, optimized to cover 4 orders of magnitude dynamic range.
| Detector | Size | Time resolution | Energy range |
| BGO/PMT* | 15 x 15 x 3.2 cm3 | 0.5 us | 300 keV – 40 MeV |
| LYSO/SiPM | 5 x 5 x 5 cm3 | 0.1 us | 300 keV – 40 MeV |
| LYSO/SiPM | 1 x 1 x 1 cm3 | 0.1 us | > 300 keV - counter |
| LYSO/SiPM | 0.3 x 0.3 x 1 cm3 | 0.1 us | > 300 keV - counter |
* From BGO/PMT (Photomultiplier Tube) we will receive real-time 1 second resolution data to identify gamma-ray glows and instruct the pilot to return to the cell
PI: Nikolai Østgaard
Team: Martino Marisaldi, Kjetil Ullaland, Shiming Yang, Bilal Qureshi, Jens Søndergaard, Bendik Husa
References
N. Østgaard , H. J. Christian, J. E. Grove, D. Sarria, A. Mezentsev, P. Kochkin, N. Lehtinen, M. Quick, S. Al-Nussirat, E. Wulf, G. Genov, K. Ullaland, M. Marisaldi, S. Yang, R. J., Blakeslee Gamma-ray glow observations at 20 km altitude, J. Geophys. Res., doi: 10.1029/2019JD030312, June 2019
P. Kochkin, N. Østgaard, H. J. Christian,, J. E. Grove, M. Quick, S. Al-Nussirat, E. Wulf, S. Yang , G. Genov, K. Ullaland, M. Marisaldi, N. Lehtinen, A. Mezentsev, D. Sarria, A rapid Gamma-Ray Glow flux reduction observed from 20 km altitude, J. Geophys. Res., doi: 10.1029/2020JD033467, April 2021
(Shiming/Jens to provide images for this section.)
iStorm
The in-Situ Thunderstorm Observer for Radiation Mechanisms, iSTORM, is a gamma-ray spectrometer optimized to make sensitive measurements of bright, fast transients in the nuclear gamma-ray band (~100 keV to >5 MeV). Designed and built by the US Naval Research Laboratory, iSTORM is a highly-segmented array of fast, high-resolution inorganic scintillators. The large total area provides high sensitivity, while the high segmentation and fast scintillation decay time preserves that large area for bright TGFs, which would paralyze a single detector of equal area. The high spectral resolution enables sensitive searches for 511 keV emission from annihilation of secondary positrons created in Terrestrial Electron Beams (TEBs) and the 2.2 MeV line from capture of secondary neutrons from intense TGFs.
| Detector | Quantity | Size | Time resolution | Energy range |
| CeBr3 / SiPM | 32 | 2.5Ø x 2.5 cm3 | <1 us | ~100 keV – 5 MeV |
| Plastic / SiPM | 1 | 1 x 1 x 1 cm3 | <1 us | >100 keV |
| SiPM array | 1 | 2.5Ø cm | <1 us | n/a |
iSTORM comprises an array of 32 CeBr3 scintillators, each 25 mm diameter by 25 mm length, and one 25 mm x 25 mm x 25 mm plastic scintillator cube. Each scintillator is read out by a custom array of silicon photomultipliers (SiPMs), which provide low-noise, high-gain amplification in a compact, low-voltage package. One additional bare SiPM array in a dark box tests for radio-frequency pickup in the instrument electronics.
Signals from each SiPM array are digitized by a commercial front-end board with ASICs that provide dual-gain preamplifiers, shaping, and peak-detect circuitry appropriate for fast scintillators with SiPM readout. A GPS receiver enables precise time-tagging of individual photons. Thermostatically controlled heaters provide thermal control, and instrument temperatures are logged by an array of thermistors.
iSTORM stores the time-tagged event-list data and housekeeping information for post-flight downloading and analysis. The instrument will fly on a NASA ER-2 research aircraft over Central America and the Caribbean at 20 km altitude as part of ALOFT mission.
Work on iSTORM at NRL is supported by ONR 6.1 Base Program funds.
PI: Eric Grove, NRL
Optical Instruments
Fly’s Eye Geostationary Lightning Mapper (GLM) Simulator (FEGS)
The Fly’s Eye GLM Simulator (FEGS) is an airborne array of multi-spectral radiometers optimized to measure the optical emission from lightning. These radiometers observe spectral emission from a variety of temperature regimes over a nominal spatial footprint of 10 x 10 km2 and with a spatial resolution of 2 x 2 km2. With a temporal resolution of 10 microseconds, FEGS adds the capability to investigate sub-millisecond lightning energetics to the NASA Airborne Earth Science program. Recent upgrades have improved FEGS sensitivity and radiometric precision as well as expanded spectral observations into the ultraviolet and shortwave infrared. When flown with its complementary suite of instruments (the ALOFT package), including a two-channel electric field change meter (EFCM) and high-energy scintillator packages, ALOFT observes lightning radiation signatures that span from radio frequencies to gamma-ray emission.
| CWL [nm] | Emission [nm] | FWHM [nm] | Species |
| 340 | 337.1 | 10 | N2 |
| 500 | 500.5 | 10 | NII |
| 700 | Broadband | 800 | multiple |
| 780 | 777.4 | 10 | OI |
| 1570 | multiple | 130 | NI |
FEGS YouTube Video: https://www.youtube.com/watch?v=QOZklnl_9r8
Electric Field Sensors
Electric Field Change Meter (EFCM)
The Electric Field Change Meter (EFCM) on the ALOFT package is a two-channel (fast and slow) antenna that measures the derivative of the electric field impulse produced by lightning. The fast channel is designed to isolate the radiative component of the lightning discharge field while the slow channel is optimized to observe the electrostatic field component. The EFCM has multiple sensitivity ranges that are selectable during flight and samples with 16-bit resolution.
| Sample Rate | Decay Time Constant | |
| Fast Channel | 10 MHz | 100 us |
| Slow Channel | 1 MHz | 150 ms |
PI: Hugh Christian
Lightning Instrument Package (LIP)
The Lightning Instrument Package (LIP) consists of seven rotating vane electric field mills on the ER-2 aircraft to observe electric fields generated by clouds and storms, as well as rapid changes in electric field due to lightning occurrence. LIP measures the vector electric field in the atmosphere and the charge induced on the aircraft using the processing and calibration technique in Mach and Koshak (2007). Properly calibrated on the aircraft, LIP can reliably measure fields lower than 1 V m-1. Effects on the derived vertical electric field due to aircraft charging are generally 5% or less, with a maximum upper error of 10% (Mach et al., 2009). LIP’s role in ALOFT is to characterize the electric field produced in storms that generate gamma-ray glows and TGFs. LIP will also provide valuable context on electricity generation to growing storms prior to their first lightning flash.
More information on LIP can be found here: https://ghrc.nsstc.nasa.gov/home/micro-articles/instrument-lightning-ins...
PI: Christopher Schultz
Co-PI: Richard Blakeslee, Monte Bateman, Douglas Mach
References
Mach, D. M., and W. J. Koshak (2007), General matrix inversion technique for the calibration of electric field sensor arrays on aircraft platforms, J. Atmos. And Oceanic Tech., 24, 1576-1587
Mach, D. M., R. J. Blakeslee, M. G. Bateman, and J. C. Bailey (2009), Electric fields, conductivity, and estimated currents from aircraft overflights of electrified clouds, J. Geophys. Res., 114, D10204, doi:10.1029/2008JD011495
Cloud Characterization Instruments
Advanced Microwave Precipitation Radiometer (AMPR)
The Advanced Microwave Precipitation Radiometer (AMPR) passively measures total power at 10.7, 19.35, 37.1, and 85.5 GHz. It scans cross-track with two orthogonally polarized channels per frequency, mapping out a ~40-km wide swath below the ER-2 as it flies. Within this swath AMPR can retrieve vertically integrated information about precipitation, ice and liquid water contents, atmospheric water vapor, and winds near the ocean surface. AMPR’s role in ALOFT is to measure the structure, evolution, and environment of thunderstorms that produce gamma-ray glows and TGFs.
More information about AMPR can be found at https://weather.ndc.nasa.gov/ampr/.
Cloud Radar System (CRS)
The CRS is a 94 GHz (W-band; 3 mm wavelength) Doppler radar developed for autonomous operation in the NASA ER-2 high-altitude aircraft and for ground-based operation. It provides high-resolution profiles of reflectivity and Doppler velocity in clouds and has important applications to atmospheric remote sensing studies.
Read more about CRS here. | Scientific article on CRS
PI: Gerry Heymsfield
X-band Radar (EXRAD)
- X-band Doppler radar to replace EDOP
- Conical scanning and fixed nadir beams
- 3D precipitation and wind measurments
- Ocean surface winds
- Operation from ER-2 or Global Hawk
- For studies of atmospheric composition and tropical storms as well as providing validation for GPM and ACE missions
Link to website | Scientific article
PI: Gerry Heymsfield
Conically Scanning Sub-millimeter-wave Imaging Radiometer (CoSSIR)
The Configurable Scanning Submillimeter-wave Instrument/Radiometer (CoSSIR) is an airborne, 16-channel total power imaging radiometer that was primarily developed for the measurement of ice clouds.
PI: Rachael Kroodsma