Validation of aerosol measurements by the satellite sensors SAM II and SAGE

The satellite sensors SAM II and SAGE have been developing a global data base on stratospheric aerosols since they were launched in October 1978 and February 1979, respectively. The validity of this data base has been tested by numerous comparisons with other measurements made by lidars, balloon-borne particle counters, and aircraft-borne impactors and filters. Because the satellite sensors measure extinction and the correlative sensors measure other properties (e.g., backscatter, number, mass), special techniques are required to convert each measured property to other properties and to quantify conversion uncertainties and measurement uncertainties. Use of these techniques in two major comparative experiments shows that the SAM II and SAGE extinction measurements agree with each other and with values derived from dustsonde, lidar, and filter measurements. In addition, the comparative experiments have highlighted the uncertainties of each type of sensor and stimulated further efforts to reduce these uncertainties.     

A balloon-borne sun-tracking multichannel photometer for atmospheric aerosol measurements

A balloon borne multichannel photometer for measurement of atmospheric scattering in the near ultraviolet and the visible wavelength regions has been developed at the Physical Research Laboratory, Ahmedabad for study of the size distribution and number density of aerosols at tropospheric and lower stratospheric altitudes. The instrumentation involves tracking the sun in elevation and scanning in azimuth. The payload was recently flown on a 100 kg. balloon from the Hyderabad Balloon Facility on 18 April 1984. The balloon reached a float altitude of 35 km and good quality data has been obtained from an altitude of 6 km upto float altitude. Data analysis is still in progress. The present paper details the instrument design and presents a few illustrations of the instrument performance from this flight.     

A comparison of two different types of geosynchronous satellite measurements during the 1989 solar proton events.

The proton telescope aboard the GOES-7 satellite continuously records the proton flux at geosynchronous orbit, and therefore provides a direct measurement of the energetic protons arriving during solar energetic particle (SEP) events. Microelectronic devices are susceptible to single event upset (SEU) caused by both energetic protons and galactic cosmic ray (GCR) ions. Some devices are so sensitive that their upsets can be used as a dosimetric indicator of a high fluence of particles. The 93L422 1K SRAM is one such device. Eight of them are on the TDRS-1 satellite in geosynchronous orbit, and collectively they had been experiencing 1-2 upset/day due to the GCR background. During the large SEP events of 1989 the upset rate increased dramatically, up to about 250 for the week of 19 Oct, due to the arrival of the SEP protons. Using the GOES proton spectra, the proton-induced SEU cross section curve for the 93L422 and the shielding distribution around the 93L422, the calculated upsets based on the GOES satellite data compared well against the log of measured upsets on TDRS-1.     

Rocket-borne measurements of atmospheric infrared emissions by spectrometric techniques

As part of the MAP/WINE Campaign 1983/84 a liquid helium cooled infrared grating spectrometer measured night zenith radiances of CO₂, O₃, and H₂O in the mesosphere and lower thermosphere. From a comparison of the measured spectral radiances with results from LTE radiative transfer calculations atmospheric temperatures and concentration profiles of H₂O and O₃ were determined, showing some interesting features. The ozone densities obtained appear to contradict model predictions based upon the assumption that ozone is in photochemical equilibrium at mesospheric heights. Since the ozone density distribution shows quite similar structures as the vertical wind profile, transport effects seem to play a major role in the mesospheric ozone formation.     

Satellite measurements of atmospheric composition

Since 1978 a number of satellite borne sensors have been used to measure the composition of the earth's atmosphere. These include the LIMS and SAMS instruments on the Nimbus 7 satellite (launched in October 1978), the SAGE instrument on the AEM2 satellite (launched in february 1979) and various instruments on the SME spacecraft (launched October 1981). For many species, these have provided the first abundance measurements with high spatial and temporal resolution and with global coverage. In this paper the composition measurements that have become available from these programs will be reviewed. The paper will then describe some recent studies that have made use of the new data. As it is the exclusive subject of another invited paper, ozone will not be discussed in in any detail.     

A middle atmosphere temperature reference model from satellite measurements

Temperature fields in the stratosphere and mesosphere have been derived from radiance measurements made by the Nimbus 5 SCR, the Nimbus 6 PMR, and the Nimbus 7 SAMS and LIMS radiometers. These instruments cover different latitude and height ranges and different times during the 1973–1983 period. The problems of combining different data sets are discussed, and examples from a proposed model atmosphere for the stratosphere and mesosphere are presented. The model is given in terms of zonal means and amplitude and phase of zonal waves 1 and 2 for temperature and geopotential height, as functions of latitude and pressure for each calendar month. Comparisons are made with the CIRA 1972 and the Koshelkov Southern Hemisphere models and with the SAMS results and in-situ rocket/radio sondes.     

Determination of aerosol optical depth from ground measurements

The methods used to determine the aerosol optical depth as a function of wavelength are briefly described and discussed. Some results from the operational network of the World Meteorological Organization and other, more research oriented studies, are reviewed and critically analysed to assess the reliability and accuracy of such determinations and their value as ground truth measurements for space applications.     

Validation of 9.6 μm ozone transmittances by spectral radiance satellite measurements

The accuracy of atmospheric transmittances is important in remote sensing applications. In this paper the atmospheric ozone transmittances in the 1042 cm^?1 ozone band were calculated for different temperatures and ozone profiles using line-by-line integration method. The absorption line parameters were taken from McClatchey's line parameter compilation. The transmittances were used to derive the main characteristics of the atmospheric ozone profile and the total ozone amount from radiance measurements of Meteor satellites.     

Definition of the lower hybrid frequency by active wave methods on the intercosmos-24 satellite and comparison of these data with mass-spectrometric measurements

The lower hybrid resonance (LHR) frequency estimated from the mass-spectrometer data is compared with measurements using spectrograms of VLF noise excited by both natural sources and through active wave stimulation of the surrounding plasma. The measurements are from the Intercosmos 24 satellite taken over a 2 year period from 1989–1991.     

Calculations of the planetary albedo from satellite radiance measurements

The concept to estimate space averages of the reflected solar exitance at the top of the atmosphere (TOA) from narrow field of view satellite instruments is presented. The largest errors, of about 2–25 %, in the estimated exitance are induced by the bidirectional function to convert radiances to exitances.     

A new model for atmospheric radiation under clear sky condition at various altitudes

Atmospheric radiation is one of the major factors that dominate the thermal behaviors of aerostats. A high-performance model is needed to evaluate the atmospheric radiation. Based on the atmospheric radiation database containing 24,862 data points compiled from 7 stations with the elevation from sea level to 2373 m and the reference code MODTRAN, a new atmospheric radiation model is proposed using regression and optimization software. It has excellent prediction accuracy with the coefficient of determination of 0.94, the root mean square error of 15.1 W/m², and the mean absolute percentage error of 4.13% for the database. Comparison with the well-known existing model shows that the new model has the highest prediction accuracy. The new model predictions agree with the MODTRAN calculations at various altitudes very well, and thus it can be used for estimating the thermal performances of a high altitude aerostat.     

International comparison of satellite winds — An update

Winds obtained from geostationary satellites are compared with each other and with rawinsondes. These comparisons serve as a periodic quality check of satellite cloud motions (or winds) set up by the CGMS (Coordination for Geostationary Meteorological Satellites). Differences are taken between colocated cloud motions observed by adjacent satellites in areas of overlapping coverage (Type 1) and between colocated rawinsondes and cloud motions within the field of view of each individual satellite (Type 2).Among colocated satellite winds (Type 1) RMS vector difference of high clouds rarely exceed 10 mps and of low clouds, 6 mps. But, among colocated cloud and balloon vectors (Type 2), RMS vector differences are large. At high levels, differences range from 12 to 40 mps for GMS (Geostationary Meteorological Satellite) winds and from 10 to 18 mps for GOES (Geostationary Operational Environmental Satellite) winds. The greater disagreement of satellite winds with rawinsonde winds than with each other is attributed in large part to error in the assignment of cloud height especially in the presence of strong vertical shear and to a lesser extent on time differences between cloud and balloon measurements. Both Type 1 and 2 comparisons suffer from separations in distance (tolerated for purposes of establishing “colocation”) between cloud and balloon in the presence of strong horizontal shear. The discrepancy existing between GMS and GOES differences with rawinsondes is attributed primarily to differing techniques of height assignment.At low levels satellite winds departed from balloon winds by a RMS vector difference of about 6 to 9 mps which approached or exceeded the mean wind speed itself. This problem is attributed chiefly to the uncertainty of wind levels controlling the motion of the various low cloud types.     

Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques

Recent advances in satellite techniques hold great potential for mapping global gravity wave (GW) processes at various altitudes. Poor understanding of small-scale GWs has been a major limitation to numerical climate and weather models for making reliable forecasts. Observations of short-scale features have important implication for validating and improving future high-resolution numerical models. This paper summarizes recent GW observations and sensitivities from several satellite instruments, including MLS, AMSU-A, AIRS, GPS, and CLAES. It is shown in an example that mountain waves with horizontal wavelengths as short as 30 km now can be observed by AIRS, reflecting the superior horizontal resolution in these modern satellite instruments. Our studies show that MLS, AMSU-A and AIRS observations reveal similar GW characteristics, with the observed variances correlated well with background winds. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS can detect GWs with better vertical but poorer horizontal resolutions. To resolve different parts of the broad GW spectrum, both satellite limb and nadir observing techniques are needed, and a better understanding of GW complexities requires joint analyses of these data and dedicated high-resolution model simulations.     

Comparison of model predictions with LDEF satellite radiation measurements.

Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.     

Can turbidity measurements be used for the estimation of aerosol parameters?

In a previous paper the authors showed that the aerosol size distribution can be estimated with reasonable accuracy from spectral extinction measurements in a limited spectral region (λ ≤ 1 μm) only. Using the same method it will be discussed if the anticipated WMO turbidity network with four spectral channels has the potential of estimating the aerosol size distribution.     

Direct comparison of transient radiation belt topology and dynamics in 1991 based on measurements onboard Mir space station and NOAA satellite.

In March 1991 the CRRES spacecraft measured a new transient radiation belt resulting from a solar proton event and subsequent geomagnetic disturbance. The presence of this belt was also noted by dosimeter-radiometers aboard the Mir space station (approx. 400 km, 51 degrees orbit) and by particle telescopes on the NOAA-10 spacecraft (850 km, 98 degrees). This event provides a unique opportunity to compare particle flux and dose measurements made by different instruments in different orbits under changing conditions. We present here a comparison of the measurements made by the different detectors. We discuss the topology and dynamics of the transient radiation belt over a period of more than one year.     

Selection of sensors and spectral bands of marine observation satellite (MOS) — 1

After trading off the proposed requirements by the Committee on Earth Observation Satellite Development, cost and time for development of sensors, spacecraft and launch vehicle, the following sensors were selected for Marine Observation Satellite (MOS) - 1.(1) Four channel visible and near IR sensor (MESSR) with 50 meter resolution. (2) Four channel visible and thermal IR sensor (VTIR) with 0.9 km (visible) and 2.7 km (IR) resolution respectively. Out of three IR channels, two channels are atmospheric window channels while the third channel is water vapor absorption band. (3) Two channel microwave scanning radiometer (MSR) with responsivity in 23.8 and 31.4 GHz respectively. (4) Data collection system.     

Energy deposition in the polar ionosphere as determined by measurements aboard ‘INTERCOSMOS-BULGARIA-1300’ satellite

Data were obtained from the measurements of optical emissions, ion drift, DC magnetic field and energetic particles, on board INTERCOSMOS - BULGARIA - 1300 satellite. In two cases of night-time passes through auroral oval, an estimate has been made of the energy input by particle precipitation and Joule heating. In order to determine the Joule heating, the Pedersen currents flowing in the lower ionosphere were determined. In orbits 231 and 203 Pedersen currents of 0.94 Am^?1 and 0.71 am^?1 were observed. From these values estimates of Joule heating rates of2 × 10^?7Wm^?3 and8 × 10^?7Wm^?3 were obtained. The integral energy deposited by the precipitated particles was also estimated in the current systems regions. The possibility for identification of the auroral electrojet based only on satellite data is pointed out.