Compact thermal imager: a flight demonstration of infrared technology for Earth observations

During 2019, an infrared camera, the compact thermal imager (CTI), recorded 15 million images of the Earth from the International Space Station. CTI is based on strained-layer superlattice (SLS) detector technology. The camera covered the spectral range from 3 to 11 µm in two spectral channels, 3.3-5.4 and 7.8-10.7 µm. Individual image frames were 26×21km² projected on the ground, with 82 m pixel resolution. A frame time of 2.54 s created continuous image swaths with a 13% along-track image overlap. Upper limits determined on the ground and in flight for the electronic offset, read noise, and dark current demonstrated the stability of the SLS detector and camera over many months. Temperature calibration was established using a combination of preflight and in-flight measurements. A narrowband approximation of temperature as a function of photon counts produced an analytic relationship covering a temperature range of 0°-400°C. Examples of CTI images illustrate temperature retrievals over sea ice, urban and agricultural areas, desert, and wildfires.

A human-driven decline in global burned area

Fire is an essential Earth system process that alters ecosystem and atmospheric composition. Here we assessed long-term fire trends using multiple satellite data sets. We found that global burned area declined by 24.3 ± 8.8% over the past 18 years. The estimated decrease in burned area remained robust after adjusting for precipitation variability and was largest in savannas. Agricultural expansion and intensification were primary drivers of declining fire activity. Fewer and smaller fires reduced aerosol concentrations, modified vegetation structure, and increased the magnitude of the terrestrial carbon sink. Fire models were unable to reproduce the pattern and magnitude of observed declines, suggesting that they may overestimate fire emissions in future projections. Using economic and demographic variables, we developed a conceptual model for predicting fire in human-dominated landscapes.

Environment and development. Brazil's Soy Moratorium

Supply-chain governance is needed to avoid deforestation

Understorey fire frequency and the fate of burned forests in southern Amazonia

Recent drought events underscore the vulnerability of Amazon forests to understorey fires. The long-term impact of fires on biodiversity and forest carbon stocks depends on the frequency of fire damages and deforestation rates of burned forests. Here, we characterized the spatial and temporal dynamics of understorey fires (1999-2010) and deforestation (2001-2010) in southern Amazonia using new satellite-based estimates of annual fire activity (greater than 50 ha) and deforestation (greater than 10 ha). Understorey forest fires burned more than 85 500 km(2) between 1999 and 2010 (2.8% of all forests). Forests that burned more than once accounted for 16 per cent of all understorey fires. Repeated fire activity was concentrated in Mato Grosso and eastern Pará, whereas single fires were widespread across the arc of deforestation. Routine fire activity in Mato Grosso coincided with annual periods of low night-time relative humidity, suggesting a strong climate control on both single and repeated fires. Understorey fires occurred in regions with active deforestation, yet the interannual variability of fire and deforestation were uncorrelated, and only 2.6 per cent of forests that burned between 1999 and 2008 were deforested for agricultural use by 2010. Evidence from the past decade suggests that future projections of frontier landscapes in Amazonia should separately consider economic drivers to project future deforestation and climate to project fire risk.

Observation of Paramagnetic Silicon Dangling Orbitals in Luminescent Porous Silicon

We have detected two dominant paramagnetic centers in porous silicon by electron paramagnetic resonance (EPR). One of them is isotropic, assigned to a defect in amorphous silicon oxide in the porous silicon layer. The other is anisotropic, and is very much like a Pb center at a planar Si/SiO2 interface. This EPR center is unambiguously identified as an •Si≡Si3 moiety, a silicon with dangling orbital, back-bonded to three silicon atoms, by 29 Si hyperfine structure (HFS) associated with the dangling orbital, and 29 Si superHFS from three neighboring silicon atoms, as similarly observed in the usual planar surface Pb structure. The dangling orbitals are highly localized and heavily p character. The disposition of dangling orbitals is evidence that the skeletal structure of luminescent porous silicon is crystalline and has a lattice which is aligned and continuous with the wafer substrate. The possibility that these centers are the major photoluminescent killers or quenchers is not supported by our hydrogen annealing experiments.

Optical Studies of Electroluminescent Structures from Porous Silicon

Two components of the electroluminescence (EL) from porous silicon light emitting diode (LED) devices have been observed. A slower component and a faster component have been identified. The slower component has a spectral peak shifted to the red from the corresponding photoluminescence (PL) spectrum. The faster component has a spectral peak well in the infrared (IR). Optical and electrical measurements of these two components are discussed. The temperature dependence of the two EL components are presented and contrasted. Our measurements demonstrate that the two EL components and the PL result from recombination in different parts of the porous silicon structure. As the temperature is reduced below room temperature the slower EL exhibits a decrease in intensity at relatively high temperatures, suggesting a freeze out of electrical carriers due to quantum confinement, resulting in a much reduced electrical excitation of the EL.

Development of High-Efficiency Zn2SiO4:Mn Thin Films for Flat Panel Cathodoluminescent Displays

Zn2SiO4:Mn thin films were deposited and studied as thin film phosphors for flat panel cathodoluminescent displays. Crystallized films with improved electrical conductivity were obtained after conventional and rapid thermal annealings in a N2 environment at 850Xy11100 °C for 0.25 to 60 minutes. A maximum cathodoluminescent efficiency of 1.3 Lm/W was achieved under dc excitation at 1500 volts. The luminescent emission from these thin films was peaked around 525 nm. The decay time of these films was controlled in the range of 2 to 10 ms by varying the deposition and annealing parameters. The fast response time of these thin films overcomes the long decay limitation of the Zn2SiO4:Mn powder phosphor in practical display applications.

Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009)

Abstract. New burned area datasets and top-down constraints from atmospheric concentration measurements of pyrogenic gases have decreased the large uncertainty in fire emissions estimates. However, significant gaps remain in our understanding of the contribution of deforestation, savanna, forest, agricultural waste, and peat fires to total global fire emissions. Here we used a revised version of the Carnegie-Ames-Stanford-Approach (CASA) biogeochemical model and improved satellite-derived estimates of area burned, fire activity, and plant productivity to calculate fire emissions for the 1997–2009 period on a 0.5° spatial resolution with a monthly time step. For November 2000 onwards, estimates were based on burned area, active fire detections, and plant productivity from the MODerate resolution Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on the MODIS era. We used maps of burned area derived from the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and estimates of plant productivity derived from Advanced Very High Resolution Radiometer (AVHRR) observations during the same period. Average global fire carbon emissions according to this version 3 of the Global Fire Emissions Database (GFED3) were 2.0 Pg C year−1 with significant interannual variability during 1997–2001 (2.8 Pg C year−1 in 1998 and 1.6 Pg C year−1 in 2001). Globally, emissions during 2002–2007 were relatively constant (around 2.1 Pg C year−1) before declining in 2008 (1.7 Pg C year−1) and 2009 (1.5 Pg C year−1) partly due to lower deforestation fire emissions in South America and tropical Asia. On a regional basis, emissions were highly variable during 2002–2007 (e.g., boreal Asia, South America, and Indonesia), but these regional differences canceled out at a global level. During the MODIS era (2001–2009), most carbon emissions were from fires in grasslands and savannas (44%) with smaller contributions from tropical deforestation and degradation fires (20%), woodland fires (mostly confined to the tropics, 16%), forest fires (mostly in the extratropics, 15%), agricultural waste burning (3%), and tropical peat fires (3%). The contribution from agricultural waste fires was likely a lower bound because our approach for measuring burned area could not detect all of these relatively small fires. Total carbon emissions were on average 13% lower than in our previous (GFED2) work. For reduced trace gases such as CO and CH4, deforestation, degradation, and peat fires were more important contributors because of higher emissions of reduced trace gases per unit carbon combusted compared to savanna fires. Carbon emissions from tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C year−1. The carbon emissions from these fires may not be balanced by regrowth following fire. Our results provide the first global assessment of the contribution of different sources to total global fire emissions for the past decade, and supply the community with an improved 13-year fire emissions time series.

Resolving the structure of ionized helium in the intergalactic medium with the far ultraviolet spectroscopic explorer

The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolving power of 15,000. We resolve the He II Lyman alpha (Lyalpha) absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities N(H I) > 10(12.3) per square centimeter that account for most of the observed opacity in He II Lyalpha. The He II to H I column density ratio ranges from 1 to >1000, with an average of approximately 80. Ratios of <100 are consistent with photoionization of the absorbing gas by a hard ionizing spectrum resulting from the integrated light of quasars, but ratios of >100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Lyalpha absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.

Ultraviolet Spectra of Stars: The ultraviolet spectra of stars are discussed from both theoretical and observational viewpoints

According to theories of model stellar atmospheres only stars of spectral types from O to about B3 may be expected to be bright in the ultraviolet-wavelength region. Observations of the strong resonance lines between 911.6 and 1900 A will yield new information permitting construction of better models for the outermost layers of OB stars. However, an adequate theory of line-formation, including non-l.t.e. effects, should be used if an accurate physical representation is to result. Already it has been demonstrated beyond doubt that O and B0 supergiants are surrounded by expanding atmospheres.