NOAA / AVHRR RSGB

LEVEL1b Data Set

 

Summary:

Remote Sensing Research Group (RSGB) collects and archives 1.1 km High Resolution Picture Transmission (HRPT) Advanced Very High Resolution Radiometer (AVHRR) imagery. Original data are from the local HRPT receiving station at Bern, Switzerland (46.917° N 7.467° E). The 1.1 km resolution for all five bands of the AVHRR sensor are recorded. Data extend from June 1996 through the present for the Area covering the Europe, parts of Northern Africa and Near East. From 1984 through 1995 the archive consist mainly off NOAA – SAA level1b data. The full path data is made available for the public in JPG format using David Taylor's HRPTReader

Table of Contents:

Summary: *

1. Dataset Overview: *

2. Investigator(s): *

3. Theory of Measurements: *

4. Equipment: *

5. Data Acquisition Methods: *

6. Data Description: *

7. Data Organization: *

8. Data Manipulations: *

9. Errors: *

10. Notes: *

11. Application of the Dataset: *

12. Dataset Plans: *

13. Related Software: *

14. Data Access: *

15. Output Products and Availability: *

16. References: *

17. Document Information: *

1. Dataset Overview:

 

Dataset Identification:

Remote Sensing Research AVHRR Polar 1 km Level 1b Data Set

Dataset Introduction:

RSGB archives images from AVHRR HRPT collections at the local HRPT receiving station at Bern, Switzerland (46.917° N 7.467° E). These data provide a current and complete picture of land and cloud cover for studies related to the atmosphere and surface processes. Data from the NOAA- 12, -14, -15, -16, and –17 are recorded. Data before 1996 come from SAA (www.saa.noaa.gov).Image files consist of five bands within the visible, near-, middle-, and thermal-infrared spectral regions. Image spatial resolution is 1.1 km along swath centerlines, but degrades to several kilometers at the outer edges of the swaths. The sensor channel gains have 10-bit (0-1023) sensitivity and span the range of normal surface and atmospheric radiances in their respective bands.

Temporal coverage begins June April 1996 for the local received HRPT images, and 1984 for the SAA data provided by NOAA. Data continue through present. For the time after 1996, the frequency of spatial coverage ranges from one to several scenes per day; however, gaps exist. This data set covers the following regions of interest:

European Alps,

Carpatian Mountains

Europe

Mediterranean Sea

Northern Africa

Generally the area covered between 30°N –70°N and 20°W-40°E

 

2. Investigator(s):

Remote Sensing Research Group

Department of Geography

University of Bern

Hallerstrasse 12

3. Theory of Measurements:

Refer to .

 

4. Equipment:

 

Sensor/Instrument Description:

 

Collection Environment:

NOAA-Series Satellites

 

Source/Platform:

all active NOAA AVHRR polar-orbiting satellites

Source/Platform Mission Objectives:

Each of the NOAA polar-orbiting satellites have carried an AVHRR as one of three sensors aboard the spacecraft. AVHRR was designed for multispectral investigations of meteorological, oceanographic, and hydrologic parameters, measuring emitted and reflected radiance in four or five spectral bands, spanning the visible portion of the spectrum to the thermal infrared.

 

Key Variables:

The sensor measures emitted and reflected radiation from Earth in two visible channels and three infrared channels.

 

Principles of Operation:

Each AVHRR scan views Earth for 51.282 milliseconds, during which time each channel of the analog data output is digitized. Scans occur at the rate of 6 per second, and the sampling rate of the AVHRR sensors is 39,936 samples per second per channel. During a scan, the detectors view an internal target, cold space, and the external scene. The temperature of the internal target is monitored, and space is assumed to have a black- body temperature of 3K.

Sensor/Instrument Measurement Geometry:

The AVHRR has a cross-track scanning system which use an elliptical beryllium mirror rotating at 360 RPM about an axis parallel to the Earth. The 110.8° cross-track scan equates to a swath width of about 2700 km. This swath width is greater than the 25.3° separation between successive orbital tracks, and provides overlapping coverage. Coverage is global, twice daily, at an instantaneous field of view (IFOV) of ~1.4 milliradians, giving a ground field of view of ~1.1 km at nadir for a nominal altitude of 833 km.

 

Manufacturer of Sensor/Instrument:

ITT Aerospace

 

Calibration:

 

Specifications:

none

 

Tolerance:

The instrument is designed to maintain a constant operating temperature for the IR detectors and provide a signal-to-noise ratio (SNR) of 3:1 at 0.5% albedo.

 

Frequency of Calibration:

The thermal infrared channels are calibrated in flight using a view of a stable blackbody and space as a reference. Channels 1 and 2 have no onboard calibration capabilities, however, they are calibrated before launch.

 

Other Calibration Information:

none

 

5. Data Acquisition Methods:

Full resolution AVHRR data are read out in High Resolution Picture Transmission (HRPT) format at University of Bern, Bern Switzerland. These data are the starting point for the AVHRR RSGB SST processing. The Level-1B data are defined as radiometrically-corrected and calibrated data in physical units at full instrument resolution as acquired.

 

6. Data Description:

 

Spatial Characteristics:

The SST data are distributed in full resolution. Each data product is produced as either an ascending (daytime) or descending (nighttime) image. These products are produced as daily dataset of each satellite pass.

 

Spatial Coverage:

30°N - 70°N,20°W-40°E

 

Spatial Resolution:

1.1km

 

Projection:

Geographic, WGS84

 

Temporal Characteristics:

 

Temporal Coverage:

Varies on the reception schedule of the RSGB groundstation, typical is around 8 datasets within 24h. SAA Archive data geos back to the mid eighties with 1 dataset per day.

 

Temporal Coverage Map:

 

Temporal Resolution:

Up to 8 passes a day

 

Data Characteristics:

 

Parameter/Variable:

Level 1b images represent data from visible, near-, mid-, and thermal-infrared spectra.

 

Unit of Measurement:

Pixel values represent sensor counts or Data Numbers (DNs) that range from 0 to 1023 for each band.

 

Data Source:

AVHRR

 

Sample Data Record:

Reduced-resolution browse images are available via the RSGB AVHRR realtime website http://saturn.unibe.ch/rsbern/noaa/dw/realtime/. RSGB generates browse images for each AVHRR scene to illustrate the area of coverage.

Related Datasets:

none

7. Data Organization:

 

Data Granularity:

The basic granule is every l1b pass dataset. The data volume is ca.70MB per set

 

Data Format:

Data are stored in NOAA level 1b orbital swath format. A level 1b file contains a one-line header followed by a series of records (one for each line of the image) with navigation, calibration, time of acquisition, and other information at the beginning of each record. The records contain band-interleaved-by-pixel (BIP) image data in a "packed" format with three right-justified 10-bit radiometric measurements packed into four bytes (30 bits stored in 32 bits or four bytes). For more information, refer to the Dundee Satellite Receiving Station's NOAA Level 1B File Format Web page (http://www.sat.dundee.ac.uk/noaa1b.html) or the online NOAA Polar Orbiter Data User's Guide(http://perigee.ncdc.noaa.gov/docs/podug/index.htm).

File Naming Convention:

The following illustrates the file naming convention for AVHRR level 1b files:

Nnn_YYYYMMDDHHMM.n1b

where:

Nnn = satellite platform

N10 = NOAA-10

N11 = NOAA-11

N12 = NOAA-12

N14 = NOAA-14

N15 = NOAA-15

N16 = NOAA-16

N17 = NOAA-17

YYYYMMDD = date of acquisition (year, month, day)

HHMM = start time in UTC

Sample Data Record:

Information not available.

 

8. Data Manipulations:

On-board calibration information is included in the data stream, but it is not applied to the data. Level 1b AVHRR data are neither calibrated nor geolocated .

9. Errors:

 

Sources of Error:

Sensor noise is less of an error factor than quantization error. Calibration drift for sensors is also a known error source.

 

Quality Assessment:

none

10. Notes:

 

Limitations of the Data:

Limitations, known problems, and usage guidance are not available.

 

Known Problems with the Data:

none

 

Usage Guidance:

none

Any Other Relevant Information about the Study:

none

 

11. Application of the Dataset:

various.

 

12. Dataset Plans:

 

Description of Future Plans:

Reprocessing efforts are ongoing.

 

13. Related Software:

 

Software Description:

none

 

14. Data Access:

Contact(s) Name, Address, Telephone and E-mail:

Remote Sensing Research Group

Department of Geography

University of Bern

Hallerstr. 12 CH - 3012 Bern Switzerland

http://www.giub.unibe.ch/remsen

 

15. Output Products and Availability:

 

FTP

Products will be available by ftp pull.

 

WWW

Quicklook of products are available: http://saturn.unibe.ch/rsbern/noaa/dw/realtime/ and made with David Taylors HRPTReader

16. References:

17. Document Information:

 

Document Revision Date:

2003-06-30

 

Document Review Date:

This document is under review.

 

Document ID:

 

Citation:

Document Curator:

David Oesch

Oesch@giub.unibe.ch