Tangent Height Research Articles

Retrieval of stratospheric aerosol extinction coefficients from sun-normalized Ozone Mapper and Profiler Suite Limb Profiler (OMPS-LP) measurements

Abstract. A new retrieval approach for obtaining vertical profiles of the aerosol extinction coefficient from measurements of scattered solar light in the limb-viewing geometry made by the Ozone Mapper and Profiler Suite Limb Profiler (OMPS-LP) instrument is presented. In contrast to many other published limb-scatter retrievals, our new algorithm does not employ normalization by a limb measurement at an upper tangent height. Instead, the measured limb radiances are normalized to solar irradiance. The main advantage of this approach is an almost complete elimination of the dependence of the retrieval results on the prior aerosol extinction profile used in the retrieval. This makes the retrieval better suited for the analysis of observation scenes with highly elevated aerosol plumes, such as those that occurred after the Hunga Tonga–Hunga Ha′apai volcanic eruption in January 2022. The results from the new approach were compared to the vertical profiles of the aerosol extinction coefficients retrieved from the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) and the Optical Spectrograph and InfraRed Imaging System (OSIRIS). In general, agreement within 25 % between the different data products was observed in the 18–23 km altitude range, although larger differences were seen after very strong volcanic eruptions and wildfires. In comparison with OSIRIS, larger differences are seen at high southern latitudes (above 60° S). The new data product was used to investigate the evolution of the aerosol plume after the Hunga Tonga–Hunga Ha′apai volcanic eruption.

Global Thermospheric Infrared Response to the Mother's Day Weekend Extreme Storm of 2024

AbstractEarth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm.

Tangent height correction and sensitivity studies from SCIAMACHY limb scattering detection

Tangent height correction and sensitivity studies from SCIAMACHY limb scattering detection

Influence of Scattered Sunlight for Wind Measurements with the O2(a1Δg) Dayglow

Observing the O2(a1Δg) dayglow with the limb-viewing DASH instrument enables remote sensing of neutral wind in near space. Many advantages are gained by using this new approach, but the influence factors on measurement accuracy have not been thoroughly investigated. This paper reports the quantitative evaluation of the wind error caused by scattered sunlight. The spectral concept of the O2(a1Δg) band and the measurement technique are briefly described. A comprehensive truth model simulation that is based on atmospheric limb radiance spectra and the instrument concept are used to obtain interferogram images. The algorithm, which uses these images to retrieve the interferogram containing information solely from the target altitude, is described. The self-absorption effect is taken into account in the unraveling of the line-of-sight integration. The influence of scattered sunlight on the limb-viewing weight and signal-to-noise ratio, two definitive factors for wind definitive factors, are also described. Representative wind precision profiles and their variation with surface albedo, aerosol loading, and cloud are presented. This indicates that the random error for Doppler wind is in the range of 2–3 m/s for the tangent height range from 45–80 km, and the wind precision under 45 km suffers significantly from scattered sunlight background.

Sensitivity Analysis of Ozone Profiles Retrieved from SCIAMACHY Limb Radiance Based on the Weighted Multiplicative Algebraic Reconstruction Technique

A detailed sensitivity analysis of ozone density profile retrieval was applied to scattering solar radiance spectra measured with the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument aboard the ENVIronmental SATellite (ENVISAT). The vertical density distribution of ozone between 10 and 69 km was obtained using the weighted multiplicative algebraic reconstruction technique and the radiative transfer model for SCIAMACHY. This study investigates the error sources for the retrieved ozone profiles, which are relevant to explain the difference between two independent instruments. The numerical simulation method was adapted to quantify the impact of various error sources on the retrieval accuracy of ozone profiles. First, the tangent height (TH) registration was found to be the largest error source. Assuming an aerosol-free atmosphere, under the condition of background aerosol, the ozone profile showed a negative deviation of ~2–10% below 40 km. With an incorrect a priori profile, ozone estimates may result in a 5–10% average error at the upper and lower boundaries. The ozone retrieval error caused by the uncertainty of surface albedo, ozone absorption cross-section, temperature, pressure profile, and low clouds was relatively small. The random error caused by the disturbance of the measurement vector obeying a Gaussian distribution did not exceed 5%. Second, the estimation of various error sources for different solar zenith angles was investigated. The error sources most strongly dependent on SZAs were aerosols, surface albedo, and clouds. Finally, the error estimation of the ozone retrieval between the northern hemisphere (NH) and the southern hemisphere (SH) was investigated, revealing that there were no strong interhemispheric differences, except for cloud height. These results can be used for interpretation of instrumental comparisons and validation of SCIAMACHY ozone profiles retrieved from different algorithms in a rigorous manner.

An optimal estimation-based retrieval of upper atmospheric oxygen airglow and temperature from SCIAMACHY limb observations

Abstract. An optimal estimation-based algorithm is developed to retrieve the number density of excited oxygen (O2) molecules that generate airglow emissions near 0.76 µm (b1Σg+ or A band) and 1.27 µm (a1Δg or 1Δ band) in the upper atmosphere. Both oxygen bands are important for the remote sensing of greenhouse gases. The algorithm is applied to the limb spectra observed by the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument in both the nominal (tangent heights below ∼ 90 km) and mesosphere–lower thermosphere (MLT) modes (tangent heights spanning 50–150 km). The number densities of emitting O2 in the a1Δg band are retrieved in an altitude range of 25–100 km near-daily in 2010, providing a climatology of O2 a1Δg-band airglow emission. This climatology will help disentangle the airglow from backscattered light in nadir remote sensing of the a1Δg band. The global monthly distributions of the vertical column density of emitting O2 in a1Δg state show mainly latitudinal dependence without other discernible geographical patterns. Temperature profiles are retrieved simultaneously from the spectral shapes of the a1Δg-band airglow emission in the nominal limb mode (valid altitude range of 40–100 km) and from both a1Δg- and b1Σg+-band airglow emissions in the MLT mode (valid range of 60–105 km). The temperature retrievals from both airglow bands are consistent internally and in agreement with independent observations from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), with the absolute mean bias near or below 5 K and root mean squared error (RMSE) near or below 10 K. The retrieved emitting O2 number density and temperature provide a unique dataset for the remote sensing of greenhouse gases and constraining the chemical and physical processes in the upper atmosphere.

Numerical investigation on heat transfer enhancement and surface temperature non-uniformity improvement of spray cooling

Heat dissipation and uniform temperature distribution are crucial to the operational reliability of electronic devices. In this study, the heat transfer enhancement and surface temperature non-uniformity (STNU) improvement of spray cooling are numerically investigated by CFD. The simulated results match well with experimental data under verification conditions with the maximum relative deviation below 7%, which demonstrates the numerical reliability of the two-phase flow model based on Euler-Lagrangian approach. The results of adjusting spray height reveal that there are different optimal spray heights for the heat transfer (4 mm) and the STNU (12.81 mm), indicating that the heat transfer enhancement and STNU improvement cannot be realized simultaneously. Based on this, two methods to enhance heat transfer and reduce STNU are developed. One method is to reduce the tangent angle θ and increase the tangent height H accordingly. It shows that the θ = 30°, H = 27.59 mm case has a maximum enhancement of 24.03% in heat flux relative to the θ = 100°, H = 6.21 mm case. Moreover, for all nozzles (θ = 30°∼100°), the lower STNU is attained at respective tangent heights. The other method is spray-array jets cooling, in which 132 micro-hole jets are added around the spray. It is found that the minimum STNU is obtained by spray-array jets cooling compared with all cases of spray cooling. In addition, it weakens the evaporation, but promotes the forced convection dramatically. Based on the analysis of several average liquid film microscopic characteristics and the droplet distribution, it is concluded that the mean film velocity, thickness and droplet coverage uniformity are the keys to determine heat transfer and STNU.

A Concept of 2U Spaceborne Multichannel Heterodyne Spectroradiometer for Greenhouse Gases Remote Sensing

We present the project of a 2U CubeSat format spaceborne multichannel laser heterodyne spectroradiometer (MLHS) for studies of the Earth’s atmosphere upper layers in the near-infrared (NIR) spectral range (1258, 1528, and 1640 nm). A spaceborne MLHS operating in the solar occultation mode onboard CubeSat platform, is capable of simultaneous vertical profiling of CO2, H2O, CH4, and O2, as well as Doppler wind measurements, in the tangent heights range of 5–50 km. We considered the low Earth orbit for the MLHS deployment and analyzed the expected surface coverage and spatial resolution during one year of operations. A ground-based prototype of the MLHS for CO2 and CH4 molecular absorption measurements with an ultra-high spectral resolution of 0.0013 cm−1 is presented along with the detailed description of its analytical characteristics and capabilities. Implementation of a multichannel configuration of the heterodyne receiver (four receivers per one spectral channel) provides a significant improvement of the signal-to-noise ratio with the reasonable exposure time typical for observations in the solar occultation mode. Finally, the capability of building up a tomographic picture of sounded gas concentration distributions provided by high spectral resolution is discussed.

Model simulations of chemical effects of sprites in relation with observed HO<sub>2</sub> enhancements over sprite-producing thunderstorms

Abstract. Recently, measurements by the Superconducting Submillimeter-Wave Limb Emission Sounder (SMILES) satellite instrument have been presented which indicate an increase in mesospheric HO2 above sprite-producing thunderstorms. The aim of this paper is to compare these observations to model simulations of chemical sprite effects. A plasma chemistry model in combination with a vertical transport module was used to simulate the impact of a streamer discharge in the altitude range 70–80 km, corresponding to one of the observed sprite events. Additionally, a horizontal transport and dispersion model was used to simulate advection and expansion of the sprite air masses. The model simulations predict a production of hydrogen radicals mainly due to reactions of proton hydrates formed after the electrical discharge. The net effect is a conversion of water molecules into H+OH. This leads to increasing HO2 concentrations a few hours after the electric breakdown. Due to the modelled long-lasting increase in HO2 after a sprite discharge, an accumulation of HO2 produced by several sprites appears possible. However, the number of sprites needed to explain the observed HO2 enhancements is unrealistically large. At least for the lower measurement tangent heights, the production mechanism of HO2 predicted by the model might contribute to the observed enhancements.

Algorithm research on the atmospheric infrared ultraspectral sounder tangent height adjustment aboard on GF-5 and inversion validation

Algorithm research on the atmospheric infrared ultraspectral sounder tangent height adjustment aboard on GF-5 and inversion validation

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

Ionospheric scintillation can significantly degrade the performance and the usability of space-based communication and navigation signals. Characterization and prediction of ionospheric scintillation can be made from the Global Navigation Satellite System (GNSS) radio occultation (RO) technique using the measurement from a deep slant path where the RO tangent height (ht) is far below the ionospheric sources. In this study, the L–band S4 from the RO measurements at ht = 30 km is used to infer the amplitude scintillation on the ground. The analysis of global RO data at ht = 30 km shows that sporadic–E (Es), equatorial plasma bubbles (EPBs), and equatorial spread–F (ESF) produce most of the significant S4 enhancements, although the polar S4 is generally weak. The enhanced S4 is a strong function of local time and magnetic dip angle. The Es–induced daytime S4 tends to have a negative correlation with the solar cycle at low latitudes but a positive correlation at high latitudes. The nighttime S4 is dominated by a strong semiannual variation at low latitudes.

Tangent height determination from the N2-continuum for the Atmospheric Chemistry Experiment Fourier transform spectrometer

With inadequate information from sensors onboard the SCISAT satellite to generate accurate pointing information, tangent heights for the solar occultation measurements collected by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) are determined from features in the measured spectra. For version 4.0 processing of the ACE-FTS data, tangent heights below 18 km are generated from the N2 collision induced absorption continuum near 2500 cm−1. Because this tangent height determination requires no assumptions on CO2 concentrations in this altitude region (unlike previous processing versions), ACE-FTS version 4.0 includes retrieved CO2 volume mixing ratio profiles below 18 km as a standard product.

Neural network aided fast pointing information determination approach for occultation payloads from in-flight measurements: Algorithm design and assessment

Pointing information is decisive to solving precise profile retrieval issues from occultation measurements. Research regarding stratospheric O3 hole in Antarctic and surface O3 pollution would significantly benefit from massive occultation measurements. A neural network aided pointing information determination approach, in terms of tangent heights, is proposed to address issues requiring fast and easy-to-use determined tangent heights. The geometrical triangular iteration (GTI) algorithm in this work is based on N2 absorption microwindows, and several treatments (e.g., tangential stride generator and triangular-net optimization) are adopted. In addition, LSTM is employed to reduce time consumption and increase accuracy. Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) in-flight measurements are used to assess this approach. The comparison between the proposed algorithm and eight official products indicates a promising performance. Correlation coefficient for each orbit is greater than 0.99. The processing time is about 16.6 min per orbit with an average cost of ∼0.06. The introduction of LSTM technique demonstrates an approximate 28.49% better result, with less computation time. It costed less than 30 s to determine eight orbit tangent heights. In general, although minor issues remain, this LSTM-aided GTI algorithm is applicable in industry.

Edge, Ridge, and Blob Detection with Symmetric Molecules

We present a novel approach to the detection and characterization of edges, ridges, and blobs in two-dimensional images which exploits the symmetry properties of directionally sensitive analyzing functions in multiscale systems that are constructed in the framework of alpha-molecules. The proposed feature detectors are inspired by the notion of phase congruency, stable in the presence of noise, and by definition invariant to changes in contrast. We also show how the behavior of coefficients corresponding to differently scaled and oriented analyzing functions can be used to obtain a comprehensive characterization of the geometry of features in terms of local tangent directions, widths, and heights. The accuracy and robustness of the proposed measures are validated and compared to various state-of-the-art algorithms in extensive numerical experiments in which we consider sets of clean and distorted synthetic images that are associated with reliable ground truths. To further demonstrate the applicability, we show how the proposed ridge measure can be used to detect and characterize blood vessels in digital retinal images and how the proposed blob measure can be applied to automatically count the number of cell colonies in a Petri dish.

Assessment of Retrieved N₂O, NO₂, and HF Profiles from the Atmospheric Infrared Ultraspectral Sounder Based on Simulated Spectra.

The Atmospheric Infrared Ultraspectral Sounder (AIUS), the first high-resolution (0.02 cm−1) solar occultation sounder, aboard GF5, was launched in May 2018 from China. However, relevant studies about vertical profiles of atmospheric constituents based on its operational data were not conducted until half a year later. Due to an urgent need for Hin-orbit tests, the real spectra (called reference spectra hereafter) were substituted with simulated spectra calculated from the reference forward model (RFM) plus different random noises at different altitudes. In the generation process of the reference spectra for N2O, NO2, and HF species, ACE-FTS (Atmospheric Chemistry Experiment–Fourier Transform Spectrometer instrument on the SCISAT satellite) level 2 products replace corresponding profiles included in the atmospheric background profiles. The optimal estimation method is employed to extract N2O, NO2, and HF profiles in this study. Comparing the retrieved results with ACE-FTS level 2 products, the relative deviations for these three species are calculated. For N2O, the average relative deviation is less than 6% at altitudes below 25 km, while larger deviations are observed in the range of 25–45 km, with the maximum being at ~25%. Additionally, the difference for NO2 is less than 5% in the 20–45 km range, with a larger discrepancy found below 20 km and above 45 km; the maximum deviation reaches ±40%. For HF, the relative deviation is less than 6% for all tangent heights, implying satisfactory retrieval. The vertical resolution, averaging kernel, and number of degrees of freedom are used to assess the retrieval algorithm, which indicate that the retrieved information content is much more attributable to the reference spectra contribution than to the a priori profile. Finally, a large number of retrieval tests are performed for N2O, NO2, and HF in selected areas covering the Arctic region, northern middle latitude, tropics, southern middle latitude, and Antarctic region, and reliable results are obtained. Thus, to a great extent, the algorithm adopted in the AIUS system can process retrievals reliably and precisely.

Analysis of ionospheric structure influences on residual ionospheric errors in GNSS radio occultation bending angles based on ray tracing simulations

Abstract. The Global Navigation Satellite System (GNSS) radio occultation (RO) technique is widely used to observe the atmosphere for applications such as numerical weather prediction and global climate monitoring. The ionosphere is a major error source to RO at upper stratospheric altitudes, and a linear dual-frequency bending angle correction is commonly used to remove the first-order ionospheric effect. However, the higher-order residual ionospheric error (RIE) can still be significant, so it needs to be further mitigated for high-accuracy applications, especially from 35 km altitude upward, where the RIE is most relevant compared to the decreasing magnitude of the atmospheric bending angle. In a previous study we quantified RIEs using an ensemble of about 700 quasi-realistic end-to-end simulated RO events, finding typical RIEs at the 0.1 to 0.5 µrad noise level, but were left with 26 exceptional events with anomalous RIEs at the 1 to 10 µrad level that remained unexplained. In this study, we focused on investigating the causes of the high RIE of these exceptional events, employing detailed along-ray-path analyses of atmospheric and ionospheric refractivities, impact parameter changes, and bending angles and RIEs under asymmetric and symmetric ionospheric structures. We found that the main causes of the high RIEs are a combination of physics-based effects – where asymmetric ionospheric conditions play the primary role, more than the ionization level driven by solar activity – and technical ray tracer effects due to occasions of imperfect smoothness in ionospheric refractivity model derivatives. We also found that along-ray impact parameter variations of more than 10 to 20 m are possible due to ionospheric asymmetries and, depending on prevailing horizontal refractivity gradients, are positive or negative relative to the initial impact parameter at the GNSS transmitter. Furthermore, mesospheric RIEs are found generally higher than upper-stratospheric ones, likely due to being closer in tangent point heights to the ionospheric E layer peaking near 105 km, which increases RIE vulnerability. In the future we will further improve the along-ray modeling system to fully isolate technical from physics-based effects and to use it beyond this work for additional GNSS RO signal propagation studies.

Retrieval of ozone profiles from OMPS limb scattering observations

Abstract. This study describes a retrieval algorithm developed at the University of Bremen to obtain vertical profiles of ozone from limb observations performed by the Ozone Mapper and Profiler Suite (OMPS). This algorithm is based on the technique originally developed for use with data from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument. As both instruments make limb measurements of the scattered solar radiation in the ultraviolet (UV) and visible (Vis) spectral ranges, an underlying objective of the study is to obtain consolidated and consistent ozone profiles from the two satellites and to produce a combined data set. The retrieval algorithm uses radiances in the UV and Vis wavelength ranges normalized to the radiance at an upper tangent height to obtain ozone concentrations in the altitude range of 12–60 km. Measurements at altitudes contaminated by clouds in the instrument field of view are identified and filtered out. An independent aerosol retrieval is performed beforehand and its results are used to account for the stratospheric aerosol load in the ozone inversion. The typical vertical resolution of the retrieved profiles varies from ∼ 2.5 km at lower altitudes ( < 30 km) to ∼ 1.5 km (about 45 km) and becomes coarser at upper altitudes. The retrieval errors resulting from the measurement noise are estimated to be 1–4 % above 25 km, increasing to 10–30 % in the upper troposphere. OMPS data are processed for the whole of 2016. The results are compared with the NASA product and validated against profiles derived from passive satellite observations or measured in situ by balloon-borne sondes. Between 20 and 60 km, OMPS ozone profiles typically agree with data from the Microwave Limb Sounder (MLS) v4.2 within 5–10 %, whereas in the lower altitude range the bias becomes larger, especially in the tropics. The comparison of OMPS profiles with ozonesonde measurements shows differences within ±5 % between 13 and 30 km at northern middle and high latitudes. At southern middle and high latitudes, an agreement within 5–7 % is also achieved in the same altitude range. An unexpected bias of approximately 10–20 % is detected in the lower tropical stratosphere. The processing of the 2013 data set using the same retrieval settings and its validation against ozonesondes reveals a much smaller bias; a possible reason for this behaviour is discussed.

New Horizons Upper Limits on O2 in Pluto’s Present Day Atmosphere

Abstract The surprising discovery by the Rosetta spacecraft of molecular oxygen (O2) in the coma of comet 67P/Churyumov–Gerasimenko challenged our understanding of the inventory of this volatile species on and inside bodies from the Kuiper Belt. That discovery motivated our search for oxygen in the atmosphere of Kuiper Belt planet Pluto, because O2 is volatile even at Pluto’s surface temperatures. During the New Horizons flyby of Pluto in 2015 July, the spacecraft probed the composition of Pluto’s atmosphere using a variety of observations, including an ultraviolet solar occultation observed by the Alice UV spectrograph. As described in these reports, absorption by molecular species in Pluto’s atmosphere yielded detections of N2, as well as hydrocarbon species such as CH4, C2H2, C2H4, and C2H6. Our work here further examines this data to search for UV absorption from molecular oxygen (O2), which has a significant cross-section in the Alice spectrograph bandpass. We find no evidence for O2 absorption and place an upper limit on the total amount of O2 in Pluto’s atmosphere as a function of tangent height up to 700 km. In most of the atmosphere, this upper limit in line-of-sight abundance units is ∼3 × 1015 cm−2, which, depending on tangent height, corresponds to a mixing ratio of 10−6 to 10−4, far lower than in comet 67P/CG.

Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon

Abstract. The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on Envisat (2002–2012) performed nadir, limb, solar/lunar occultation and various monitoring measurements. The pointing information of the instrument is determined by the attitude information of the Envisat platform with its star trackers together with the encoder readouts of both the azimuth and the elevation scanner of SCIAMACHY. In this work, we present additional sources of attitude information from the SCIAMACHY measurements itself. The basic principle is the same as used by the star tracker: we measure the viewing direction towards celestial objects, i.e. sun and moon, to detect possible mispointings. In sun over limb port observations, we utilise the vertical scans over the solar disk. In horizontal direction, SCIAMACHY's sun follower device (SFD) is used to adjust the viewing direction. Moon over limb port measurements use for both the vertical and the horizontal direction the adjustment by the SFD. The viewing direction is steered towards the intensity centroid of the illuminated part of the lunar disk. We use reference images from the USGS Robotic Lunar Observatory (ROLO) to take into account the inhomogeneous surface and the variations by lunar libration and phase to parameterise the location of the intensity centroid from the observation geometry. Solar observations through SCIAMACHY's so-called sub-solar port (with a viewing direction closely to zenith) also use the SFD in the vertical direction. In the horizontal direction the geometry of the port defines the viewing direction. Using these three type of measurements, we fit improved mispointing parameters by minimising the pointing offsets in elevation and azimuth. The geolocation of all retrieved products will benefit from this; the tangent heights are especially improved. The altitudes assigned to SCIAMACHY's solar occultation measurements are changed in the range of −130 to −330 m, the lunar occultation measurements are changed in the range of 0 to +130 m and the limb measurements are changed in the range of −50 to +60 m (depending on season, altitude and azimuth angle). The horizontal location of the tangent point is changed by about 5 km for all measurements. These updates are implemented in version 9 of the SCIAMACHY Level 1b products and Level 2 version 7 (based on L1b version 9).

Altitude registration of limb-scattered radiation

Abstract. One of the largest constraints to the retrieval of accurate ozone profiles from UV backscatter limb sounding sensors is altitude registration. Two methods, the Rayleigh scattering attitude sensing (RSAS) and absolute radiance residual method (ARRM), are able to determine altitude registration to the accuracy necessary for long-term ozone monitoring. The methods compare model calculations of radiances to measured radiances and are independent of onboard tracking devices. RSAS determines absolute altitude errors, but, because the method is susceptible to aerosol interference, it is limited to latitudes and time periods with minimal aerosol contamination. ARRM, a new technique introduced in this paper, can be applied across all seasons and altitudes. However, it is only appropriate for relative altitude error estimates. The application of RSAS to Limb Profiler (LP) measurements from the Ozone Mapping and Profiler Suite (OMPS) on board the Suomi NPP (SNPP) satellite indicates tangent height (TH) errors greater than 1 km with an absolute accuracy of ±200 m. Results using ARRM indicate a ∼ 300 to 400 m intra-orbital TH change varying seasonally ±100 m, likely due to either errors in the spacecraft pointing or in the geopotential height (GPH) data that we use in our analysis. ARRM shows a change of ∼ 200 m over ∼ 5 years with a relative accuracy (a long-term accuracy) of ±100 m outside the polar regions.